Elixir v1.9.2 Kernel View Source
Kernel
is Elixir's default environment.
It mainly consists of:
- basic language primitives, such as arithmetic operators, spawning of processes, data type handling, etc.
- macros for control-flow and defining new functionality (modules, functions, and so on)
- guard checks for augmenting pattern matching
You can use Kernel
functions/macros without the Kernel
prefix anywhere in
Elixir code as all its functions and macros are automatically imported. For
example, in IEx:
iex> is_number(13)
true
If you don't want to import a function or macro from Kernel
, use the :except
option and then list the function/macro by arity:
import Kernel, except: [if: 2, unless: 2]
See Kernel.SpecialForms.import/2
for more information on importing.
Elixir also has special forms that are always imported and
cannot be skipped. These are described in Kernel.SpecialForms
.
The standard library
Kernel
provides the basic capabilities the Elixir standard library
is built on top of. It is recommended to explore the standard library
for advanced functionality. Here are the main groups of modules in the
standard library (this list is not a complete reference, see the
documentation sidebar for all entries).
Built-in types
The following modules handle Elixir built-in data types:
Atom
- literal constants with a name (true
,false
, andnil
are atoms)Float
- numbers with floating point precisionFunction
- a reference to code chunk, created with thefn/1
special formInteger
- whole numbers (not fractions)List
- collections of a variable number of elements (linked lists)Map
- collections of key-value pairsProcess
- light-weight threads of executionPort
- mechanisms to interact with the external worldTuple
- collections of a fixed number of elements
There are two data types without an accompanying module:
- Bitstring - a sequence of bits, created with
Kernel.SpecialForms.<<>>/1
. When the number of bits is divisible by 8, they are called binaries and can be manipulated with Erlang's:binary
module - Reference - a unique value in the runtime system, created with
make_ref/0
Data types
Elixir also provides other data types that are built on top of the types listed above. Some of them are:
Date
-year-month-day
structs in a given calendarDateTime
- date and time with time zone in a given calendarException
- data raised from errors and unexpected scenariosMapSet
- unordered collections of unique elementsNaiveDateTime
- date and time without time zone in a given calendarKeyword
- lists of two-element tuples, often representing optional valuesRange
- inclusive ranges between two integersRegex
- regular expressionsString
- UTF-8 encoded binaries representing charactersTime
-hour:minute:second
structs in a given calendarURI
- representation of URIs that identify resourcesVersion
- representation of versions and requirements
System modules
Modules that interface with the underlying system, such as:
IO
- handles input and outputFile
- interacts with the underlying file systemPath
- manipulates file system pathsSystem
- reads and writes system information
Protocols
Protocols add polymorphic dispatch to Elixir. They are contracts
implementable by data types. See defprotocol/2
for more information on
protocols. Elixir provides the following protocols in the standard library:
Collectable
- collects data into a data typeEnumerable
- handles collections in Elixir. TheEnum
module provides eager functions for working with collections, theStream
module provides lazy functionsInspect
- converts data types into their programming language representationList.Chars
- converts data types to their outside world representation as charlists (non-programming based)String.Chars
- converts data types to their outside world representation as strings (non-programming based)
Process-based and application-centric functionality
The following modules build on top of processes to provide concurrency, fault-tolerance, and more.
Agent
- a process that encapsulates mutable stateApplication
- functions for starting, stopping and configuring applicationsGenServer
- a generic client-server APIRegistry
- a key-value process-based storageSupervisor
- a process that is responsible for starting, supervising and shutting down other processesTask
- a process that performs computationsTask.Supervisor
- a supervisor for managing tasks exclusively
Supporting documents
Elixir documentation also includes supporting documents under the "Pages" section. Those are:
- Compatibility and Deprecations - lists compatibility between every Elixir version and Erlang/OTP, release schema; lists all deprecated functions, when they were deprecated and alternatives
- Guards - an introduction to guards and extensions
- Library Guidelines - general guidelines, anti-patterns, and rules for those writing libraries
- Naming Conventions - naming conventions for Elixir code
- Operators - lists all Elixir operators and their precedence
- Syntax Reference - the language syntax reference
- Typespecs- types and function specifications, including list of types
- Unicode Syntax - outlines Elixir support for Unicode
- Writing Documentation - guidelines for writing documentation in Elixir
Guards
This module includes the built-in guards used by Elixir developers.
They are a predefined set of functions and macros that augment pattern
matching, typically invoked after the when
operator. For example:
def drive(%User{age: age}) when age >= 16 do
...
end
The clause above will only be invoked if the user's age is more than or equal to 16. A more complete introduction to guards is available in the Guards page.
Inlining
Some of the functions described in this module are inlined by
the Elixir compiler into their Erlang counterparts in the
:erlang
module.
Those functions are called BIFs (built-in internal functions)
in Erlang-land and they exhibit interesting properties, as some
of them are allowed in guards and others are used for compiler
optimizations.
Most of the inlined functions can be seen in effect when capturing the function:
iex> &Kernel.is_atom/1
&:erlang.is_atom/1
Those functions will be explicitly marked in their docs as "inlined by the compiler".
Truthy and falsy values
Besides the booleans true
and false
Elixir also has the
concept of a "truthy" or "falsy" value.
- a value is truthy when it is neither
false
nornil
- a value is falsy when it is either
false
ornil
Elixir has functions, like and/2
, that only work with
booleans, but also functions that work with these
truthy/falsy values, like &&/2
and !/1
.
Examples
We can check the truthiness of a value by using the !/1
function twice.
Truthy values:
iex> !!true
true
iex> !!5
true
iex> !![1,2]
true
iex> !!"foo"
true
Falsy values (of which there are exactly two):
iex> !!false
false
iex> !!nil
false
Link to this section Summary
Guards
Returns true
if the two terms are not equal.
Returns true
if the two terms are not exactly equal.
Arithmetic multiplication.
Arithmetic unary plus.
Arithmetic addition.
Arithmetic unary minus.
Arithmetic subtraction.
Arithmetic division.
Returns true
if left is less than right.
Returns true
if left is less than or equal to right.
Returns true
if the two terms are equal.
Returns true
if the two terms are exactly equal.
Returns true
if left is more than right.
Returns true
if left is more than or equal to right.
Returns an integer or float which is the arithmetical absolute value of number
.
Boolean and.
Extracts the part of the binary starting at start
with length length
.
Binaries are zero-indexed.
Returns an integer which is the size in bits of bitstring
.
Returns the number of bytes needed to contain bitstring
.
Returns the smallest integer greater than or equal to number
.
Performs an integer division.
Gets the element at the zero-based index
in tuple
.
Returns the largest integer smaller than or equal to number
.
Returns the head of a list. Raises ArgumentError
if the list is empty.
Checks if the element on the left-hand side is a member of the collection on the right-hand side.
Returns true
if term
is an atom; otherwise returns false
.
Returns true
if term
is a binary; otherwise returns false
.
Returns true
if term
is a bitstring (including a binary); otherwise returns false
.
Returns true
if term
is either the atom true
or the atom false
(i.e.,
a boolean); otherwise returns false
.
Returns true
if term
is a floating-point number; otherwise returns false
.
Returns true
if term
is a function; otherwise returns false
.
Returns true
if term
is a function that can be applied with arity
number of arguments;
otherwise returns false
.
Returns true
if term
is an integer; otherwise returns false
.
Returns true
if term
is a list with zero or more elements; otherwise returns false
.
Returns true
if term
is a map; otherwise returns false
.
Returns true
if term
is nil
, false
otherwise.
Returns true
if term
is either an integer or a floating-point number;
otherwise returns false
.
Returns true
if term
is a PID (process identifier); otherwise returns false
.
Returns true
if term
is a port identifier; otherwise returns false
.
Returns true
if term
is a reference; otherwise returns false
.
Returns true
if term
is a tuple; otherwise returns false
.
Returns the length of list
.
Returns the size of a map.
Returns an atom representing the name of the local node.
If the node is not alive, :nonode@nohost
is returned instead.
Returns the node where the given argument is located.
The argument can be a PID, a reference, or a port.
If the local node is not alive, :nonode@nohost
is returned.
Boolean not.
Boolean or.
Computes the remainder of an integer division.
Rounds a number to the nearest integer.
Returns the PID (process identifier) of the calling process.
Returns the tail of a list. Raises ArgumentError
if the list is empty.
Returns the integer part of number
.
Returns the size of a tuple.
Functions
Boolean not.
Provides a short-circuit operator that evaluates and returns
the second expression only if the first one evaluates to to a truthy value
(neither false
nor nil
). Returns the first expression
otherwise.
Concatenates a proper list and a term, returning a list.
Removes the first occurrence of an element on the left list for each element on the right.
Returns a range with the specified first
and last
integers.
Concatenates two binaries.
Matches the term on the left
against the regular expression or string on the
right
.
Reads and writes attributes of the current module.
When used inside quoting, marks that the given alias should not be hygienized. This means the alias will be expanded when the macro is expanded.
Invokes the given anonymous function fun
with the list of
arguments args
.
Invokes the given function from module
with the list of
arguments args
.
Returns the binding for the given context as a keyword list.
Defines a function with the given name and body.
Defines a function that delegates to another module.
Defines an exception.
Generates a macro suitable for use in guard expressions.
Generates a private macro suitable for use in guard expressions.
Defines an implementation for the given protocol.
Defines a macro with the given name and body.
Defines a private macro with the given name and body.
Defines a module given by name with the given contents.
Makes the given functions in the current module overridable.
Defines a private function with the given name and body.
Defines a protocol.
Defines a struct.
Destructures two lists, assigning each term in the right one to the matching term in the left one.
Stops the execution of the calling process with the given reason.
Returns true
if module
is loaded and contains a
public function
with the given arity
, otherwise false
.
Gets a value and updates a nested data structure via the given path
.
Gets a value and updates a nested structure.
Gets a value from a nested structure.
Provides an if/2
macro.
Inspects the given argument according to the Inspect
protocol.
The second argument is a keyword list with options to control
inspection.
Returns true
if module
is loaded and contains a
public macro
with the given arity
, otherwise false
.
Returns an almost unique reference.
A convenience macro that checks if the right side (an expression) matches the left side (a pattern).
Returns the biggest of the two given terms according to Erlang's term ordering.
Returns the smallest of the two given terms according to Erlang's term ordering.
Pops a key from the nested structure via the given path
.
Pops a key from the given nested structure.
Puts value
at the given zero-based index
in tuple
.
Puts a value in a nested structure via the given path
.
Puts a value in a nested structure.
Raises an exception.
Raises an exception.
Raises an exception preserving a previous stacktrace.
Raises an exception preserving a previous stacktrace.
Sends a message to the given dest
and returns the message.
Handles the sigil ~C
for charlists.
Handles the sigil ~D
for dates.
Handles the sigil ~N
for naive date times.
Handles the sigil ~R
for regular expressions.
Handles the sigil ~S
for strings.
Handles the sigil ~T
for times.
Handles the sigil ~U
to create a UTC DateTime
.
Handles the sigil ~W
for list of words.
Handles the sigil ~c
for charlists.
Handles the sigil ~r
for regular expressions.
Handles the sigil ~s
for strings.
Handles the sigil ~w
for list of words.
Spawns the given function and returns its PID.
Spawns the given function fun
from the given module
passing it the given
args
and returns its PID.
Spawns the given function, links it to the current process, and returns its PID.
Spawns the given function fun
from the given module
passing it the given
args
, links it to the current process, and returns its PID.
Spawns the given function, monitors it and returns its PID and monitoring reference.
Spawns the given module and function passing the given args, monitors it and returns its PID and monitoring reference.
Creates and updates structs.
Similar to struct/2
but checks for key validity.
A non-local return from a function.
Converts the given term to a charlist according to the List.Chars
protocol.
Converts the argument to a string according to the
String.Chars
protocol.
Provides an unless
macro.
Updates a nested structure via the given path
.
Updates a key in a nested structure.
Uses the given module in the current context.
When used inside quoting, marks that the given variable should not be hygienized.
Pipe operator.
Provides a short-circuit operator that evaluates and returns the second
expression only if the first one does not evaluate to a truthy value (that is,
it is either nil
or false
). Returns the first expression otherwise.
Link to this section Guards
Specs
Returns true
if the two terms are not equal.
This operator considers 1 and 1.0 to be equal. For match
comparison, use !==/2
instead.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 != 2
true
iex> 1 != 1.0
false
Specs
Returns true
if the two terms are not exactly equal.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 !== 2
true
iex> 1 !== 1.0
true
Specs
integer() * integer() :: integer()
float() * float() :: float()
integer() * float() :: float()
float() * integer() :: float()
Arithmetic multiplication.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 * 2
2
Specs
+value :: value when value: number()
Arithmetic unary plus.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> +1
1
Specs
integer() + integer() :: integer()
float() + float() :: float()
integer() + float() :: float()
float() + integer() :: float()
Arithmetic addition.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 + 2
3
Specs
Arithmetic unary minus.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> -2
-2
Specs
integer() - integer() :: integer()
float() - float() :: float()
integer() - float() :: float()
float() - integer() :: float()
Arithmetic subtraction.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 - 2
-1
Specs
Arithmetic division.
The result is always a float. Use div/2
and rem/2
if you want
an integer division or the remainder.
Raises ArithmeticError
if right
is 0 or 0.0.
Allowed in guard tests. Inlined by the compiler.
Examples
1 / 2
#=> 0.5
-3.0 / 2.0
#=> -1.5
5 / 1
#=> 5.0
7 / 0
#=> ** (ArithmeticError) bad argument in arithmetic expression
Specs
Returns true
if left is less than right.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 < 2
true
Specs
Returns true
if left is less than or equal to right.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 <= 2
true
Specs
Returns true
if the two terms are equal.
This operator considers 1 and 1.0 to be equal. For stricter
semantics, use ===/2
instead.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 == 2
false
iex> 1 == 1.0
true
Specs
Returns true
if the two terms are exactly equal.
The terms are only considered to be exactly equal if they
have the same value and are of the same type. For example,
1 == 1.0
returns true
, but since they are of different
types, 1 === 1.0
returns false
.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 === 2
false
iex> 1 === 1.0
false
Specs
Returns true
if left is more than right.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 > 2
false
Specs
Returns true
if left is more than or equal to right.
All terms in Elixir can be compared with each other.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> 1 >= 2
false
Specs
Returns an integer or float which is the arithmetical absolute value of number
.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> abs(-3.33)
3.33
iex> abs(-3)
3
Boolean and.
If left
is false
, returns false
; otherwise returns right
.
Requires only the left
operand to be a boolean since it short-circuits. If
the left
operand is not a boolean, an ArgumentError
exception is raised.
Allowed in guard tests.
Examples
iex> true and false
false
iex> true and "yay!"
"yay!"
Specs
binary_part(binary(), non_neg_integer(), integer()) :: binary()
Extracts the part of the binary starting at start
with length length
.
Binaries are zero-indexed.
If start
or length
reference in any way outside the binary, an
ArgumentError
exception is raised.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> binary_part("foo", 1, 2)
"oo"
A negative length
can be used to extract bytes that come before the byte
at start
:
iex> binary_part("Hello", 5, -3)
"llo"
Specs
bit_size(bitstring()) :: non_neg_integer()
Returns an integer which is the size in bits of bitstring
.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> bit_size(<<433::16, 3::3>>)
19
iex> bit_size(<<1, 2, 3>>)
24
Specs
byte_size(bitstring()) :: non_neg_integer()
Returns the number of bytes needed to contain bitstring
.
That is, if the number of bits in bitstring
is not divisible by 8, the
resulting number of bytes will be rounded up (by excess). This operation
happens in constant time.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> byte_size(<<433::16, 3::3>>)
3
iex> byte_size(<<1, 2, 3>>)
3
Specs
Returns the smallest integer greater than or equal to number
.
If you want to perform ceil operation on other decimal places,
use Float.ceil/2
instead.
Allowed in guard tests. Inlined by the compiler.
Specs
div(integer(), neg_integer() | pos_integer()) :: integer()
Performs an integer division.
Raises an ArithmeticError
exception if one of the arguments is not an
integer, or when the divisor
is 0
.
div/2
performs truncated integer division. This means that
the result is always rounded towards zero.
If you want to perform floored integer division (rounding towards negative infinity),
use Integer.floor_div/2
instead.
Allowed in guard tests. Inlined by the compiler.
Examples
div(5, 2)
#=> 2
div(6, -4)
#=> -1
div(-99, 2)
#=> -49
div(100, 0)
#=> ** (ArithmeticError) bad argument in arithmetic expression
Specs
elem(tuple(), non_neg_integer()) :: term()
Gets the element at the zero-based index
in tuple
.
It raises ArgumentError
when index is negative or it is out of range of the tuple elements.
Allowed in guard tests. Inlined by the compiler.
Examples
tuple = {:foo, :bar, 3}
elem(tuple, 1)
#=> :bar
elem({}, 0)
#=> ** (ArgumentError) argument error
elem({:foo, :bar}, 2)
#=> ** (ArgumentError) argument error
Specs
Returns the largest integer smaller than or equal to number
.
If you want to perform floor operation on other decimal places,
use Float.floor/2
instead.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns the head of a list. Raises ArgumentError
if the list is empty.
It works with improper lists.
Allowed in guard tests. Inlined by the compiler.
Examples
hd([1, 2, 3, 4])
#=> 1
hd([])
#=> ** (ArgumentError) argument error
hd([1 | 2])
#=> 1
Checks if the element on the left-hand side is a member of the collection on the right-hand side.
Examples
iex> x = 1
iex> x in [1, 2, 3]
true
This operator (which is a macro) simply translates to a call to
Enum.member?/2
. The example above would translate to:
Enum.member?([1, 2, 3], x)
Elixir also supports left not in right
, which evaluates to
not(left in right)
:
iex> x = 1
iex> x not in [1, 2, 3]
false
Guards
The in/2
operator (as well as not in
) can be used in guard clauses as
long as the right-hand side is a range or a list. In such cases, Elixir will
expand the operator to a valid guard expression. For example:
when x in [1, 2, 3]
translates to:
when x === 1 or x === 2 or x === 3
When using ranges:
when x in 1..3
translates to:
when is_integer(x) and x >= 1 and x <= 3
Note that only integers can be considered inside a range by in
.
AST considerations
left not in right
is parsed by the compiler into the AST:
{:not, _, [{:in, _, [left, right]}]}
This is the same AST as not(left in right)
.
Additionally, Macro.to_string/2
will translate all occurrences of
this AST to left not in right
.
Specs
Returns true
if term
is an atom; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a binary; otherwise returns false
.
A binary always contains a complete number of bytes.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> is_binary("foo")
true
iex> is_binary(<<1::3>>)
false
Specs
Returns true
if term
is a bitstring (including a binary); otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> is_bitstring("foo")
true
iex> is_bitstring(<<1::3>>)
true
Specs
Returns true
if term
is either the atom true
or the atom false
(i.e.,
a boolean); otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a floating-point number; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a function; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
is_function(term(), non_neg_integer()) :: boolean()
Returns true
if term
is a function that can be applied with arity
number of arguments;
otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> is_function(fn x -> x * 2 end, 1)
true
iex> is_function(fn x -> x * 2 end, 2)
false
Specs
Returns true
if term
is an integer; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a list with zero or more elements; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a map; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Returns true
if term
is nil
, false
otherwise.
Allowed in guard clauses.
Examples
iex> is_nil(1)
false
iex> is_nil(nil)
true
Specs
Returns true
if term
is either an integer or a floating-point number;
otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a PID (process identifier); otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a port identifier; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a reference; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns true
if term
is a tuple; otherwise returns false
.
Allowed in guard tests. Inlined by the compiler.
Specs
length(list()) :: non_neg_integer()
Returns the length of list
.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> length([1, 2, 3, 4, 5, 6, 7, 8, 9])
9
Specs
map_size(map()) :: non_neg_integer()
Returns the size of a map.
The size of a map is the number of key-value pairs that the map contains.
This operation happens in constant time.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> map_size(%{a: "foo", b: "bar"})
2
Specs
node() :: node()
Returns an atom representing the name of the local node.
If the node is not alive, :nonode@nohost
is returned instead.
Allowed in guard tests. Inlined by the compiler.
Specs
Returns the node where the given argument is located.
The argument can be a PID, a reference, or a port.
If the local node is not alive, :nonode@nohost
is returned.
Allowed in guard tests. Inlined by the compiler.
Specs
not true :: false
not false :: true
Boolean not.
arg
must be a boolean; if it's not, an ArgumentError
exception is raised.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> not false
true
Boolean or.
If left
is true
, returns true
; otherwise returns right
.
Requires only the left
operand to be a boolean since it short-circuits.
If the left
operand is not a boolean, an ArgumentError
exception is
raised.
Allowed in guard tests.
Examples
iex> true or false
true
iex> false or 42
42
Specs
rem(integer(), neg_integer() | pos_integer()) :: integer()
Computes the remainder of an integer division.
rem/2
uses truncated division, which means that
the result will always have the sign of the dividend
.
Raises an ArithmeticError
exception if one of the arguments is not an
integer, or when the divisor
is 0
.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> rem(5, 2)
1
iex> rem(6, -4)
2
Specs
Rounds a number to the nearest integer.
If the number is equidistant to the two nearest integers, rounds away from zero.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> round(5.6)
6
iex> round(5.2)
5
iex> round(-9.9)
-10
iex> round(-9)
-9
iex> round(2.5)
3
iex> round(-2.5)
-3
Specs
self() :: pid()
Returns the PID (process identifier) of the calling process.
Allowed in guard clauses. Inlined by the compiler.
Specs
tl(nonempty_maybe_improper_list(elem, tail)) :: maybe_improper_list(elem, tail) | tail when elem: term(), tail: term()
Returns the tail of a list. Raises ArgumentError
if the list is empty.
It works with improper lists.
Allowed in guard tests. Inlined by the compiler.
Examples
tl([1, 2, 3, :go])
#=> [2, 3, :go]
tl([])
#=> ** (ArgumentError) argument error
tl([:one])
#=> []
tl([:a, :b | :c])
#=> [:b | :c]
tl([:a | %{b: 1}])
#=> %{b: 1}
Specs
Returns the integer part of number
.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> trunc(5.4)
5
iex> trunc(-5.99)
-5
iex> trunc(-5)
-5
Specs
tuple_size(tuple()) :: non_neg_integer()
Returns the size of a tuple.
This operation happens in constant time.
Allowed in guard tests. Inlined by the compiler.
Examples
iex> tuple_size({:a, :b, :c})
3
Link to this section Functions
Boolean not.
Receives any argument (not just booleans) and returns true
if the argument
is false
or nil
; returns false
otherwise.
Not allowed in guard clauses.
Examples
iex> !Enum.empty?([])
false
iex> !List.first([])
true
Provides a short-circuit operator that evaluates and returns
the second expression only if the first one evaluates to to a truthy value
(neither false
nor nil
). Returns the first expression
otherwise.
Not allowed in guard clauses.
Examples
iex> Enum.empty?([]) && Enum.empty?([])
true
iex> List.first([]) && true
nil
iex> Enum.empty?([]) && List.first([1])
1
iex> false && throw(:bad)
false
Note that, unlike and/2
, this operator accepts any expression
as the first argument, not only booleans.
Specs
list() ++ term() :: maybe_improper_list()
Concatenates a proper list and a term, returning a list.
The complexity of a ++ b
is proportional to length(a)
, so avoid repeatedly
appending to lists of arbitrary length, e.g. list ++ [element]
.
Instead, consider prepending via [element | rest]
and then reversing.
If the right
operand is not a proper list, it returns an improper list.
If the left
operand is not a proper list, it raises ArgumentError
.
Inlined by the compiler.
Examples
iex> [1] ++ [2, 3]
[1, 2, 3]
iex> 'foo' ++ 'bar'
'foobar'
# returns an improper list
iex> [1] ++ 2
[1 | 2]
# returns a proper list
iex> [1] ++ [2]
[1, 2]
# improper list on the right will return an improper list
iex> [1] ++ [2 | 3]
[1, 2 | 3]
Specs
Removes the first occurrence of an element on the left list for each element on the right.
The complexity of a -- b
is proportional to length(a) * length(b)
,
meaning that it will be very slow if both a
and b
are long lists.
In such cases, consider converting each list to a MapSet
and using
MapSet.difference/2
.
Inlined by the compiler.
Examples
iex> [1, 2, 3] -- [1, 2]
[3]
iex> [1, 2, 3, 2, 1] -- [1, 2, 2]
[3, 1]
Returns a range with the specified first
and last
integers.
If last is larger than first, the range will be increasing from first to last. If first is larger than last, the range will be decreasing from first to last. If first is equal to last, the range will contain one element, which is the number itself.
Examples
iex> 0 in 1..3
false
iex> 1 in 1..3
true
iex> 2 in 1..3
true
iex> 3 in 1..3
true
Concatenates two binaries.
Examples
iex> "foo" <> "bar"
"foobar"
The <>/2
operator can also be used in pattern matching (and guard clauses) as
long as the left argument is a literal binary:
iex> "foo" <> x = "foobar"
iex> x
"bar"
x <> "bar" = "foobar"
would have resulted in a CompileError
exception.
Specs
Matches the term on the left
against the regular expression or string on the
right
.
Returns true
if left
matches right
(if it's a regular expression)
or contains right
(if it's a string).
Examples
iex> "abcd" =~ ~r/c(d)/
true
iex> "abcd" =~ ~r/e/
false
iex> "abcd" =~ "bc"
true
iex> "abcd" =~ "ad"
false
iex> "abcd" =~ ""
true
Reads and writes attributes of the current module.
The canonical example for attributes is annotating that a module
implements an OTP behaviour, such as GenServer
:
defmodule MyServer do
@behaviour GenServer
# ... callbacks ...
end
By default Elixir supports all the module attributes supported by Erlang, but custom attributes can be used as well:
defmodule MyServer do
@my_data 13
IO.inspect(@my_data) #=> 13
end
Unlike Erlang, such attributes are not stored in the module by default since
it is common in Elixir to use custom attributes to store temporary data that
will be available at compile-time. Custom attributes may be configured to
behave closer to Erlang by using Module.register_attribute/3
.
Finally, notice that attributes can also be read inside functions:
defmodule MyServer do
@my_data 11
def first_data, do: @my_data
@my_data 13
def second_data, do: @my_data
end
MyServer.first_data()
#=> 11
MyServer.second_data()
#=> 13
It is important to note that reading an attribute takes a snapshot of
its current value. In other words, the value is read at compilation
time and not at runtime. Check the Module
module for other functions
to manipulate module attributes.
When used inside quoting, marks that the given alias should not be hygienized. This means the alias will be expanded when the macro is expanded.
Check Kernel.SpecialForms.quote/2
for more information.
Specs
Invokes the given anonymous function fun
with the list of
arguments args
.
Inlined by the compiler.
Examples
iex> apply(fn x -> x * 2 end, [2])
4
Specs
Invokes the given function from module
with the list of
arguments args
.
apply/3
is used to invoke functions where the module, function
name or arguments are defined dynamically at runtime. For this
reason, you can't invoke macros using apply/3
, only functions.
Inlined by the compiler.
Examples
iex> apply(Enum, :reverse, [[1, 2, 3]])
[3, 2, 1]
Returns the binding for the given context as a keyword list.
In the returned result, keys are variable names and values are the corresponding variable values.
If the given context
is nil
(by default it is), the binding for the
current context is returned.
Examples
iex> x = 1
iex> binding()
[x: 1]
iex> x = 2
iex> binding()
[x: 2]
iex> binding(:foo)
[]
iex> var!(x, :foo) = 1
1
iex> binding(:foo)
[x: 1]
Defines a function with the given name and body.
Examples
defmodule Foo do
def bar, do: :baz
end
Foo.bar()
#=> :baz
A function that expects arguments can be defined as follows:
defmodule Foo do
def sum(a, b) do
a + b
end
end
In the example above, a sum/2
function is defined; this function receives
two arguments and returns their sum.
Default arguments
\\
is used to specify a default value for a parameter of a function. For
example:
defmodule MyMath do
def multiply_by(number, factor \\ 2) do
number * factor
end
end
MyMath.multiply_by(4, 3)
#=> 12
MyMath.multiply_by(4)
#=> 8
The compiler translates this into multiple functions with different arities,
here MyMath.multiply_by/1
and MyMath.multiply_by/2
, that represent cases when
arguments for parameters with default values are passed or not passed.
When defining a function with default arguments as well as multiple explicitly declared clauses, you must write a function head that declares the defaults. For example:
defmodule MyString do
def join(string1, string2 \\ nil, separator \\ " ")
def join(string1, nil, _separator) do
string1
end
def join(string1, string2, separator) do
string1 <> separator <> string2
end
end
Note that \\
can't be used with anonymous functions because they
can only have a sole arity.
Function and variable names
Function and variable names have the following syntax: A lowercase ASCII letter or an underscore, followed by any number of lowercase or uppercase ASCII letters, numbers, or underscores. Optionally they can end in either an exclamation mark or a question mark.
For variables, any identifier starting with an underscore should indicate an unused variable. For example:
def foo(bar) do
[]
end
#=> warning: variable bar is unused
def foo(_bar) do
[]
end
#=> no warning
def foo(_bar) do
_bar
end
#=> warning: the underscored variable "_bar" is used after being set
rescue
/catch
/after
/else
Function bodies support rescue
, catch
, after
, and else
as Kernel.SpecialForms.try/1
does. For example, the following two functions are equivalent:
def format(value) do
try do
format!(value)
catch
:exit, reason -> {:error, reason}
end
end
def format(value) do
format!(value)
catch
:exit, reason -> {:error, reason}
end
Defines a function that delegates to another module.
Functions defined with defdelegate/2
are public and can be invoked from
outside the module they're defined in, as if they were defined using def/2
.
Therefore, defdelegate/2
is about extending the current module's public API.
If what you want is to invoke a function defined in another module without
using its full module name, then use alias/2
to shorten the module name or use
import/2
to be able to invoke the function without the module name altogether.
Delegation only works with functions; delegating macros is not supported.
Check def/2
for rules on naming and default arguments.
Options
:to
- the module to dispatch to.:as
- the function to call on the target given in:to
. This parameter is optional and defaults to the name being delegated (funs
).
Examples
defmodule MyList do
defdelegate reverse(list), to: Enum
defdelegate other_reverse(list), to: Enum, as: :reverse
end
MyList.reverse([1, 2, 3])
#=> [3, 2, 1]
MyList.other_reverse([1, 2, 3])
#=> [3, 2, 1]
Defines an exception.
Exceptions are structs backed by a module that implements
the Exception
behaviour. The Exception
behaviour requires
two functions to be implemented:
exception/1
- receives the arguments given toraise/2
and returns the exception struct. The default implementation accepts either a set of keyword arguments that is merged into the struct or a string to be used as the exception's message.message/1
- receives the exception struct and must return its message. Most commonly exceptions have a message field which by default is accessed by this function. However, if an exception does not have a message field, this function must be explicitly implemented.
Since exceptions are structs, the API supported by defstruct/1
is also available in defexception/1
.
Raising exceptions
The most common way to raise an exception is via raise/2
:
defmodule MyAppError do
defexception [:message]
end
value = [:hello]
raise MyAppError,
message: "did not get what was expected, got: #{inspect(value)}"
In many cases it is more convenient to pass the expected value to
raise/2
and generate the message in the Exception.exception/1
callback:
defmodule MyAppError do
defexception [:message]
@impl true
def exception(value) do
msg = "did not get what was expected, got: #{inspect(value)}"
%MyAppError{message: msg}
end
end
raise MyAppError, value
The example above shows the preferred strategy for customizing exception messages.
Specs
Generates a macro suitable for use in guard expressions.
It raises at compile time if the definition uses expressions that aren't allowed in guards, and otherwise creates a macro that can be used both inside or outside guards.
Note the convention in Elixir is to name functions/macros allowed in
guards with the is_
prefix, such as is_list/1
. If, however, the
function/macro returns a boolean and is not allowed in guards, it should
have no prefix and end with a question mark, such as Keyword.keyword?/1
.
Example
defmodule Integer.Guards do
defguard is_even(value) when is_integer(value) and rem(value, 2) == 0
end
defmodule Collatz do
@moduledoc "Tools for working with the Collatz sequence."
import Integer.Guards
@doc "Determines the number of steps `n` takes to reach `1`."
# If this function never converges, please let me know what `n` you used.
def converge(n) when n > 0, do: step(n, 0)
defp step(1, step_count) do
step_count
end
defp step(n, step_count) when is_even(n) do
step(div(n, 2), step_count + 1)
end
defp step(n, step_count) do
step(3 * n + 1, step_count + 1)
end
end
Specs
Generates a private macro suitable for use in guard expressions.
It raises at compile time if the definition uses expressions that aren't allowed in guards, and otherwise creates a private macro that can be used both inside or outside guards in the current module.
Similar to defmacrop/2
, defguardp/1
must be defined before its use
in the current module.
Defines an implementation for the given protocol.
See the Protocol
module for more information.
Defines a macro with the given name and body.
Macros must be defined before its usage.
Check def/2
for rules on naming and default arguments.
Examples
defmodule MyLogic do
defmacro unless(expr, opts) do
quote do
if !unquote(expr), unquote(opts)
end
end
end
require MyLogic
MyLogic.unless false do
IO.puts("It works")
end
Defines a private macro with the given name and body.
Private macros are only accessible from the same module in which they are defined.
Private macros must be defined before its usage.
Check defmacro/2
for more information, and check def/2
for rules on
naming and default arguments.
Defines a module given by name with the given contents.
This macro defines a module with the given alias
as its name and with the
given contents. It returns a tuple with four elements:
:module
- the module name
- the binary contents of the module
- the result of evaluating the contents block
Examples
iex> defmodule Foo do
...> def bar, do: :baz
...> end
iex> Foo.bar()
:baz
Nesting
Nesting a module inside another module affects the name of the nested module:
defmodule Foo do
defmodule Bar do
end
end
In the example above, two modules - Foo
and Foo.Bar
- are created.
When nesting, Elixir automatically creates an alias to the inner module,
allowing the second module Foo.Bar
to be accessed as Bar
in the same
lexical scope where it's defined (the Foo
module). This only happens
if the nested module is defined via an alias.
If the Foo.Bar
module is moved somewhere else, the references to Bar
in
the Foo
module need to be updated to the fully-qualified name (Foo.Bar
) or
an alias has to be explicitly set in the Foo
module with the help of
Kernel.SpecialForms.alias/2
.
defmodule Foo.Bar do
# code
end
defmodule Foo do
alias Foo.Bar
# code here can refer to "Foo.Bar" as just "Bar"
end
Dynamic names
Elixir module names can be dynamically generated. This is very useful when working with macros. For instance, one could write:
defmodule String.to_atom("Foo#{1}") do
# contents ...
end
Elixir will accept any module name as long as the expression passed as the
first argument to defmodule/2
evaluates to an atom.
Note that, when a dynamic name is used, Elixir won't nest the name under
the current module nor automatically set up an alias.
Reserved module names
If you attempt to define a module that already exists, you will get a warning saying that a module has been redefined.
There are some modules that Elixir does not currently implement but it may be implement in the future. Those modules are reserved and defining them will result in a compilation error:
defmodule Any do
# code
end
#=> ** (CompileError) iex:1: module Any is reserved and cannot be defined
Elixir reserves the following module names: Elixir
, Any
, BitString
,
PID
, and Reference
.
Makes the given functions in the current module overridable.
An overridable function is lazily defined, allowing a developer to override it.
Macros cannot be overridden as functions and vice-versa.
Example
defmodule DefaultMod do
defmacro __using__(_opts) do
quote do
def test(x, y) do
x + y
end
defoverridable test: 2
end
end
end
defmodule InheritMod do
use DefaultMod
def test(x, y) do
x * y + super(x, y)
end
end
As seen as in the example above, super
can be used to call the default
implementation.
If @behaviour
has been defined, defoverridable
can also be called with a
module as an argument. All implemented callbacks from the behaviour above the
call to defoverridable
will be marked as overridable.
Example
defmodule Behaviour do
@callback foo :: any
end
defmodule DefaultMod do
defmacro __using__(_opts) do
quote do
@behaviour Behaviour
def foo do
"Override me"
end
defoverridable Behaviour
end
end
end
defmodule InheritMod do
use DefaultMod
def foo do
"Overridden"
end
end
Defines a private function with the given name and body.
Private functions are only accessible from within the module in which they are
defined. Trying to access a private function from outside the module it's
defined in results in an UndefinedFunctionError
exception.
Check def/2
for more information.
Examples
defmodule Foo do
def bar do
sum(1, 2)
end
defp sum(a, b), do: a + b
end
Foo.bar()
#=> 3
Foo.sum(1, 2)
#=> ** (UndefinedFunctionError) undefined function Foo.sum/2
Defines a protocol.
See the Protocol
module for more information.
Defines a struct.
A struct is a tagged map that allows developers to provide default values for keys, tags to be used in polymorphic dispatches and compile time assertions.
To define a struct, a developer must define both __struct__/0
and
__struct__/1
functions. defstruct/1
is a convenience macro which
defines such functions with some conveniences.
For more information about structs, please check Kernel.SpecialForms.%/2
.
Examples
defmodule User do
defstruct name: nil, age: nil
end
Struct fields are evaluated at compile-time, which allows
them to be dynamic. In the example below, 10 + 11
is
evaluated at compile-time and the age field is stored
with value 21
:
defmodule User do
defstruct name: nil, age: 10 + 11
end
The fields
argument is usually a keyword list with field names
as atom keys and default values as corresponding values. defstruct/1
also supports a list of atoms as its argument: in that case, the atoms
in the list will be used as the struct's field names and they will all
default to nil
.
defmodule Post do
defstruct [:title, :content, :author]
end
Deriving
Although structs are maps, by default structs do not implement
any of the protocols implemented for maps. For example, attempting
to use a protocol with the User
struct leads to an error:
john = %User{name: "John"}
MyProtocol.call(john)
** (Protocol.UndefinedError) protocol MyProtocol not implemented for %User{...}
defstruct/1
, however, allows protocol implementations to be
derived. This can be done by defining a @derive
attribute as a
list before invoking defstruct/1
:
defmodule User do
@derive [MyProtocol]
defstruct name: nil, age: 10 + 11
end
MyProtocol.call(john) #=> works
For each protocol in the @derive
list, Elixir will assert the protocol has
been implemented for Any
. If the Any
implementation defines a
__deriving__/3
callback, the callback will be invoked and it should define
the implementation module. Otherwise an implementation that simply points to
the Any
implementation is automatically derived. For more information on
the __deriving__/3
callback, see Protocol.derive/3
.
Enforcing keys
When building a struct, Elixir will automatically guarantee all keys belongs to the struct:
%User{name: "john", unknown: :key}
** (KeyError) key :unknown not found in: %User{age: 21, name: nil}
Elixir also allows developers to enforce certain keys must always be given when building the struct:
defmodule User do
@enforce_keys [:name]
defstruct name: nil, age: 10 + 11
end
Now trying to build a struct without the name key will fail:
%User{age: 21}
** (ArgumentError) the following keys must also be given when building struct User: [:name]
Keep in mind @enforce_keys
is a simple compile-time guarantee
to aid developers when building structs. It is not enforced on
updates and it does not provide any sort of value-validation.
Types
It is recommended to define types for structs. By convention such type
is called t
. To define a struct inside a type, the struct literal syntax
is used:
defmodule User do
defstruct name: "John", age: 25
@type t :: %__MODULE__{name: String.t(), age: non_neg_integer}
end
It is recommended to only use the struct syntax when defining the struct's
type. When referring to another struct it's better to use User.t
instead of
%User{}
.
The types of the struct fields that are not included in %User{}
default to
term()
(see term/0
).
Structs whose internal structure is private to the local module (pattern
matching them or directly accessing their fields should not be allowed) should
use the @opaque
attribute. Structs whose internal structure is public should
use @type
.
Destructures two lists, assigning each term in the right one to the matching term in the left one.
Unlike pattern matching via =
, if the sizes of the left
and right lists don't match, destructuring simply stops
instead of raising an error.
Examples
iex> destructure([x, y, z], [1, 2, 3, 4, 5])
iex> {x, y, z}
{1, 2, 3}
In the example above, even though the right list has more entries than the
left one, destructuring works fine. If the right list is smaller, the
remaining elements are simply set to nil
:
iex> destructure([x, y, z], [1])
iex> {x, y, z}
{1, nil, nil}
The left-hand side supports any expression you would use on the left-hand side of a match:
x = 1
destructure([^x, y, z], [1, 2, 3])
The example above will only work if x
matches the first value in the right
list. Otherwise, it will raise a MatchError
(like the =
operator would
do).
Specs
Stops the execution of the calling process with the given reason.
Since evaluating this function causes the process to terminate, it has no return value.
Inlined by the compiler.
Examples
When a process reaches its end, by default it exits with
reason :normal
. You can also call exit/1
explicitly if you
want to terminate a process but not signal any failure:
exit(:normal)
In case something goes wrong, you can also use exit/1
with
a different reason:
exit(:seems_bad)
If the exit reason is not :normal
, all the processes linked to the process
that exited will crash (unless they are trapping exits).
OTP exits
Exits are used by the OTP to determine if a process exited abnormally or not. The following exits are considered "normal":
exit(:normal)
exit(:shutdown)
exit({:shutdown, term})
Exiting with any other reason is considered abnormal and treated as a crash. This means the default supervisor behaviour kicks in, error reports are emitted, etc.
This behaviour is relied on in many different places. For example,
ExUnit
uses exit(:shutdown)
when exiting the test process to
signal linked processes, supervision trees and so on to politely
shut down too.
CLI exits
Building on top of the exit signals mentioned above, if the process started by the command line exits with any of the three reasons above, its exit is considered normal and the Operating System process will exit with status 0.
It is, however, possible to customize the operating system exit signal by invoking:
exit({:shutdown, integer})
This will cause the operating system process to exit with the status given by
integer
while signaling all linked Erlang processes to politely
shut down.
Any other exit reason will cause the operating system process to exit with
status 1
and linked Erlang processes to crash.
Specs
Returns true
if module
is loaded and contains a
public function
with the given arity
, otherwise false
.
Note that this function does not load the module in case
it is not loaded. Check Code.ensure_loaded/1
for more
information.
Inlined by the compiler.
Examples
iex> function_exported?(Enum, :map, 2)
true
iex> function_exported?(Enum, :map, 10)
false
iex> function_exported?(List, :to_string, 1)
true
Gets a value and updates a nested data structure via the given path
.
This is similar to get_and_update_in/3
, except the path is extracted
via a macro rather than passing a list. For example:
get_and_update_in(opts[:foo][:bar], &{&1, &1 + 1})
Is equivalent to:
get_and_update_in(opts, [:foo, :bar], &{&1, &1 + 1})
This also works with nested structs and the struct.path.to.value
way to specify
paths:
get_and_update_in(struct.foo.bar, &{&1, &1 + 1})
Note that in order for this macro to work, the complete path must always be visible by this macro. See the Paths section below.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> get_and_update_in(users["john"].age, &{&1, &1 + 1})
{27, %{"john" => %{age: 28}, "meg" => %{age: 23}}}
Paths
A path may start with a variable, local or remote call, and must be followed by one or more:
foo[bar]
- accesses the keybar
infoo
; in casefoo
is nil,nil
is returnedfoo.bar
- accesses a map/struct field; in case the field is not present, an error is raised
Here are some valid paths:
users["john"][:age]
users["john"].age
User.all()["john"].age
all_users()["john"].age
Here are some invalid ones:
# Does a remote call after the initial value
users["john"].do_something(arg1, arg2)
# Does not access any key or field
users
Specs
get_and_update_in( structure :: Access.t(), keys, (term() -> {get_value, update_value} | :pop) ) :: {get_value, structure :: Access.t()} when keys: [any(), ...], update_value: term(), get_value: var
Gets a value and updates a nested structure.
data
is a nested structure (that is, a map, keyword
list, or struct that implements the Access
behaviour).
The fun
argument receives the value of key
(or nil
if key
is not present) and must return one of the following values:
a two-element tuple
{get_value, new_value}
. In this case,get_value
is the retrieved value which can possibly be operated on before being returned.new_value
is the new value to be stored underkey
.:pop
, which implies that the current value underkey
should be removed from the structure and returned.
This function uses the Access
module to traverse the structures
according to the given keys
, unless the key
is a function,
which is detailed in a later section.
Examples
This function is useful when there is a need to retrieve the current value (or something calculated in function of the current value) and update it at the same time. For example, it could be used to read the current age of a user while increasing it by one in one pass:
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> get_and_update_in(users, ["john", :age], &{&1, &1 + 1})
{27, %{"john" => %{age: 28}, "meg" => %{age: 23}}}
Functions as keys
If a key is a function, the function will be invoked passing three arguments:
- the operation (
:get_and_update
) - the data to be accessed
- a function to be invoked next
This means get_and_update_in/3
can be extended to provide custom
lookups. The downside is that functions cannot be stored as keys
in the accessed data structures.
When one of the keys is a function, the function is invoked. In the example below, we use a function to get and increment all ages inside a list:
iex> users = [%{name: "john", age: 27}, %{name: "meg", age: 23}]
iex> all = fn :get_and_update, data, next ->
...> data |> Enum.map(next) |> Enum.unzip()
...> end
iex> get_and_update_in(users, [all, :age], &{&1, &1 + 1})
{[27, 23], [%{name: "john", age: 28}, %{name: "meg", age: 24}]}
If the previous value before invoking the function is nil
,
the function will receive nil
as a value and must handle it
accordingly (be it by failing or providing a sane default).
The Access
module ships with many convenience accessor functions,
like the all
anonymous function defined above. See Access.all/0
,
Access.key/2
, and others as examples.
Specs
Gets a value from a nested structure.
Uses the Access
module to traverse the structures
according to the given keys
, unless the key
is a
function, which is detailed in a later section.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> get_in(users, ["john", :age])
27
In case any of the entries in the middle returns nil
, nil
will
be returned as per the Access
module:
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> get_in(users, ["unknown", :age])
nil
Functions as keys
If a key is a function, the function will be invoked passing three arguments:
- the operation (
:get
) - the data to be accessed
- a function to be invoked next
This means get_in/2
can be extended to provide custom lookups.
The downside is that functions cannot be stored as keys in the accessed
data structures.
In the example below, we use a function to get all the maps inside a list:
iex> users = [%{name: "john", age: 27}, %{name: "meg", age: 23}]
iex> all = fn :get, data, next -> Enum.map(data, next) end
iex> get_in(users, [all, :age])
[27, 23]
If the previous value before invoking the function is nil
,
the function will receive nil
as a value and must handle it
accordingly.
The Access
module ships with many convenience accessor functions,
like the all
anonymous function defined above. See Access.all/0
,
Access.key/2
, and others as examples.
Provides an if/2
macro.
This macro expects the first argument to be a condition and the second argument to be a keyword list.
One-liner examples
if(foo, do: bar)
In the example above, bar
will be returned if foo
evaluates to
a truthy value (neither false
nor nil
). Otherwise, nil
will be
returned.
An else
option can be given to specify the opposite:
if(foo, do: bar, else: baz)
Blocks examples
It's also possible to pass a block to the if/2
macro. The first
example above would be translated to:
if foo do
bar
end
Note that do/end
become delimiters. The second example would
translate to:
if foo do
bar
else
baz
end
In order to compare more than two clauses, the cond/1
macro has to be used.
Specs
Inspects the given argument according to the Inspect
protocol.
The second argument is a keyword list with options to control
inspection.
Options
inspect/2
accepts a list of options that are internally
translated to an Inspect.Opts
struct. Check the docs for
Inspect.Opts
to see the supported options.
Examples
iex> inspect(:foo)
":foo"
iex> inspect([1, 2, 3, 4, 5], limit: 3)
"[1, 2, 3, ...]"
iex> inspect([1, 2, 3], pretty: true, width: 0)
"[1,\n 2,\n 3]"
iex> inspect("olá" <> <<0>>)
"<<111, 108, 195, 161, 0>>"
iex> inspect("olá" <> <<0>>, binaries: :as_strings)
"\"olá\\0\""
iex> inspect("olá", binaries: :as_binaries)
"<<111, 108, 195, 161>>"
iex> inspect('bar')
"'bar'"
iex> inspect([0 | 'bar'])
"[0, 98, 97, 114]"
iex> inspect(100, base: :octal)
"0o144"
iex> inspect(100, base: :hex)
"0x64"
Note that the Inspect
protocol does not necessarily return a valid
representation of an Elixir term. In such cases, the inspected result
must start with #
. For example, inspecting a function will return:
inspect(fn a, b -> a + b end)
#=> #Function<...>
The Inspect
protocol can be derived to hide certain fields
from structs, so they don't show up in logs, inspects and similar.
See the "Deriving" section of the documentation of the Inspect
protocol for more information.
Specs
Returns true
if module
is loaded and contains a
public macro
with the given arity
, otherwise false
.
Note that this function does not load the module in case
it is not loaded. Check Code.ensure_loaded/1
for more
information.
If module
is an Erlang module (as opposed to an Elixir module), this
function always returns false
.
Examples
iex> macro_exported?(Kernel, :use, 2)
true
iex> macro_exported?(:erlang, :abs, 1)
false
Specs
make_ref() :: reference()
Returns an almost unique reference.
The returned reference will re-occur after approximately 2^82 calls; therefore it is unique enough for practical purposes.
Inlined by the compiler.
Examples
make_ref()
#=> #Reference<0.0.0.135>
A convenience macro that checks if the right side (an expression) matches the left side (a pattern).
Examples
iex> match?(1, 1)
true
iex> match?(1, 2)
false
iex> match?({1, _}, {1, 2})
true
iex> map = %{a: 1, b: 2}
iex> match?(%{a: _}, map)
true
iex> a = 1
iex> match?(^a, 1)
true
match?/2
is very useful when filtering or finding a value in an enumerable:
iex> list = [a: 1, b: 2, a: 3]
iex> Enum.filter(list, &match?({:a, _}, &1))
[a: 1, a: 3]
Guard clauses can also be given to the match:
iex> list = [a: 1, b: 2, a: 3]
iex> Enum.filter(list, &match?({:a, x} when x < 2, &1))
[a: 1]
However, variables assigned in the match will not be available
outside of the function call (unlike regular pattern matching with the =
operator):
iex> match?(_x, 1)
true
iex> binding()
[]
Specs
Returns the biggest of the two given terms according to Erlang's term ordering.
If the terms compare equal, the first one is returned.
Inlined by the compiler.
Examples
iex> max(1, 2)
2
iex> max(:a, :b)
:b
Using Erlang's term ordering means that comparisons are structural and not semantic. For example, when comparing dates:
iex> max(~D[2017-03-31], ~D[2017-04-01])
~D[2017-03-31]
In the example above, max/2
returned March 31st instead of April 1st
because the structural comparison compares the day before the year. In
such cases it is common for modules to provide functions such as
Date.compare/2
that perform semantic comparison.
Specs
Returns the smallest of the two given terms according to Erlang's term ordering.
If the terms compare equal, the first one is returned.
Inlined by the compiler.
Examples
iex> min(1, 2)
1
iex> min("foo", "bar")
"bar"
Using Erlang's term ordering means that comparisons are structural and not semantic. For example, when comparing dates:
iex> min(~D[2017-03-31], ~D[2017-04-01])
~D[2017-04-01]
In the example above, min/2
returned April 1st instead of March 31st
because the structural comparison compares the day before the year. In
such cases it is common for modules to provide functions such as
Date.compare/2
that perform semantic comparison.
Pops a key from the nested structure via the given path
.
This is similar to pop_in/2
, except the path is extracted via
a macro rather than passing a list. For example:
pop_in(opts[:foo][:bar])
Is equivalent to:
pop_in(opts, [:foo, :bar])
Note that in order for this macro to work, the complete path must always
be visible by this macro. For more information about the supported path
expressions, please check get_and_update_in/2
docs.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> pop_in(users["john"][:age])
{27, %{"john" => %{}, "meg" => %{age: 23}}}
iex> users = %{john: %{age: 27}, meg: %{age: 23}}
iex> pop_in(users.john[:age])
{27, %{john: %{}, meg: %{age: 23}}}
In case any entry returns nil
, its key will be removed
and the deletion will be considered a success.
Specs
pop_in(data, [Access.get_and_update_fun(term(), data) | term(), ...]) :: {term(), data} when data: Access.container()
Pops a key from the given nested structure.
Uses the Access
protocol to traverse the structures
according to the given keys
, unless the key
is a
function. If the key is a function, it will be invoked
as specified in get_and_update_in/3
.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> pop_in(users, ["john", :age])
{27, %{"john" => %{}, "meg" => %{age: 23}}}
In case any entry returns nil
, its key will be removed
and the deletion will be considered a success.
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> pop_in(users, ["jane", :age])
{nil, %{"john" => %{age: 27}, "meg" => %{age: 23}}}
Specs
put_elem(tuple(), non_neg_integer(), term()) :: tuple()
Puts value
at the given zero-based index
in tuple
.
Inlined by the compiler.
Examples
iex> tuple = {:foo, :bar, 3}
iex> put_elem(tuple, 0, :baz)
{:baz, :bar, 3}
Puts a value in a nested structure via the given path
.
This is similar to put_in/3
, except the path is extracted via
a macro rather than passing a list. For example:
put_in(opts[:foo][:bar], :baz)
Is equivalent to:
put_in(opts, [:foo, :bar], :baz)
This also works with nested structs and the struct.path.to.value
way to specify
paths:
put_in(struct.foo.bar, :baz)
Note that in order for this macro to work, the complete path must always
be visible by this macro. For more information about the supported path
expressions, please check get_and_update_in/2
docs.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> put_in(users["john"][:age], 28)
%{"john" => %{age: 28}, "meg" => %{age: 23}}
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> put_in(users["john"].age, 28)
%{"john" => %{age: 28}, "meg" => %{age: 23}}
Specs
Puts a value in a nested structure.
Uses the Access
module to traverse the structures
according to the given keys
, unless the key
is a
function. If the key is a function, it will be invoked
as specified in get_and_update_in/3
.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> put_in(users, ["john", :age], 28)
%{"john" => %{age: 28}, "meg" => %{age: 23}}
In case any of the entries in the middle returns nil
,
an error will be raised when trying to access it next.
Raises an exception.
If the argument msg
is a binary, it raises a RuntimeError
exception
using the given argument as message.
If msg
is an atom, it just calls raise/2
with the atom as the first
argument and []
as the second argument.
If msg
is an exception struct, it is raised as is.
If msg
is anything else, raise
will fail with an ArgumentError
exception.
Examples
iex> raise "oops"
** (RuntimeError) oops
try do
1 + :foo
rescue
x in [ArithmeticError] ->
IO.puts("that was expected")
raise x
end
Raises an exception.
Calls the exception/1
function on the given argument (which has to be a
module name like ArgumentError
or RuntimeError
) passing attrs
as the
attributes in order to retrieve the exception struct.
Any module that contains a call to the defexception/1
macro automatically
implements the Exception.exception/1
callback expected by raise/2
.
For more information, see defexception/1
.
Examples
iex> raise(ArgumentError, "Sample")
** (ArgumentError) Sample
Raises an exception preserving a previous stacktrace.
Works like raise/1
but does not generate a new stacktrace.
Notice that __STACKTRACE__
can be used inside catch/rescue
to retrieve the current stacktrace.
Examples
try do
raise "oops"
rescue
exception ->
reraise exception, __STACKTRACE__
end
Raises an exception preserving a previous stacktrace.
reraise/3
works like reraise/2
, except it passes arguments to the
exception/1
function as explained in raise/2
.
Examples
try do
raise "oops"
rescue
exception ->
reraise WrapperError, [exception: exception], __STACKTRACE__
end
Specs
send(dest :: Process.dest(), message) :: message when message: any()
Sends a message to the given dest
and returns the message.
dest
may be a remote or local PID, a local port, a locally
registered name, or a tuple in the form of {registered_name, node}
for a
registered name at another node.
Inlined by the compiler.
Examples
iex> send(self(), :hello)
:hello
Handles the sigil ~C
for charlists.
It simply returns a charlist without escaping characters and without interpolations.
Examples
iex> ~C(foo)
'foo'
iex> ~C(f#{o}o)
'f\#{o}o'
Handles the sigil ~D
for dates.
The lower case ~d
variant does not exist as interpolation
and escape characters are not useful for date sigils.
More information on dates can be found in the Date
module.
Examples
iex> ~D[2015-01-13]
~D[2015-01-13]
Handles the sigil ~N
for naive date times.
The lower case ~n
variant does not exist as interpolation
and escape characters are not useful for date time sigils.
More information on naive date times can be found in the NaiveDateTime
module.
Examples
iex> ~N[2015-01-13 13:00:07]
~N[2015-01-13 13:00:07]
iex> ~N[2015-01-13T13:00:07.001]
~N[2015-01-13 13:00:07.001]
Handles the sigil ~R
for regular expressions.
It returns a regular expression pattern without escaping nor interpreting interpolations.
More information on regexes can be found in the Regex
module.
Examples
iex> Regex.match?(~R(f#{1,3}o), "f#o")
true
Handles the sigil ~S
for strings.
It simply returns a string without escaping characters and without interpolations.
Examples
iex> ~S(foo)
"foo"
iex> ~S(f#{o}o)
"f\#{o}o"
Handles the sigil ~T
for times.
The lower case ~t
variant does not exist as interpolation
and escape characters are not useful for time sigils.
More information on times can be found in the Time
module.
Examples
iex> ~T[13:00:07]
~T[13:00:07]
iex> ~T[13:00:07.001]
~T[13:00:07.001]
Handles the sigil ~U
to create a UTC DateTime
.
The lower case ~u
variant does not exist as interpolation
and escape characters are not useful for date time sigils.
The given datetime_string
must include "Z" or "00:00" offset which marks it
as UTC, otherwise an error is raised.
More information on date times can be found in the DateTime
module.
Examples
iex> ~U[2015-01-13 13:00:07Z]
~U[2015-01-13 13:00:07Z]
iex> ~U[2015-01-13T13:00:07.001+00:00]
~U[2015-01-13 13:00:07.001Z]
Handles the sigil ~W
for list of words.
It returns a list of "words" split by whitespace without escaping nor interpreting interpolations.
Modifiers
s
: words in the list are strings (default)a
: words in the list are atomsc
: words in the list are charlists
Examples
iex> ~W(foo #{bar} baz)
["foo", "\#{bar}", "baz"]
Handles the sigil ~c
for charlists.
It returns a charlist as if it was a single quoted string, unescaping characters and replacing interpolations.
Examples
iex> ~c(foo)
'foo'
iex> ~c(f#{:o}o)
'foo'
iex> ~c(f\#{:o}o)
'f\#{:o}o'
Handles the sigil ~r
for regular expressions.
It returns a regular expression pattern, unescaping characters and replacing interpolations.
More information on regular expressions can be found in the Regex
module.
Examples
iex> Regex.match?(~r(foo), "foo")
true
iex> Regex.match?(~r/abc/, "abc")
true
Handles the sigil ~s
for strings.
It returns a string as if it was a double quoted string, unescaping characters and replacing interpolations.
Examples
iex> ~s(foo)
"foo"
iex> ~s(f#{:o}o)
"foo"
iex> ~s(f\#{:o}o)
"f\#{:o}o"
Handles the sigil ~w
for list of words.
It returns a list of "words" split by whitespace. Character unescaping and interpolation happens for each word.
Modifiers
s
: words in the list are strings (default)a
: words in the list are atomsc
: words in the list are charlists
Examples
iex> ~w(foo #{:bar} baz)
["foo", "bar", "baz"]
iex> ~w(foo #{" bar baz "})
["foo", "bar", "baz"]
iex> ~w(--source test/enum_test.exs)
["--source", "test/enum_test.exs"]
iex> ~w(foo bar baz)a
[:foo, :bar, :baz]
Specs
Spawns the given function and returns its PID.
Typically developers do not use the spawn
functions, instead they use
abstractions such as Task
, GenServer
and Agent
, built on top of
spawn
, that spawns processes with more conveniences in terms of
introspection and debugging.
Check the Process
module for more process-related functions.
The anonymous function receives 0 arguments, and may return any value.
Inlined by the compiler.
Examples
current = self()
child = spawn(fn -> send(current, {self(), 1 + 2}) end)
receive do
{^child, 3} -> IO.puts("Received 3 back")
end
Specs
Spawns the given function fun
from the given module
passing it the given
args
and returns its PID.
Typically developers do not use the spawn
functions, instead they use
abstractions such as Task
, GenServer
and Agent
, built on top of
spawn
, that spawns processes with more conveniences in terms of
introspection and debugging.
Check the Process
module for more process-related functions.
Inlined by the compiler.
Examples
spawn(SomeModule, :function, [1, 2, 3])
Specs
Spawns the given function, links it to the current process, and returns its PID.
Typically developers do not use the spawn
functions, instead they use
abstractions such as Task
, GenServer
and Agent
, built on top of
spawn
, that spawns processes with more conveniences in terms of
introspection and debugging.
Check the Process
module for more process-related functions. For more
information on linking, check Process.link/1
.
The anonymous function receives 0 arguments, and may return any value.
Inlined by the compiler.
Examples
current = self()
child = spawn_link(fn -> send(current, {self(), 1 + 2}) end)
receive do
{^child, 3} -> IO.puts("Received 3 back")
end
Specs
Spawns the given function fun
from the given module
passing it the given
args
, links it to the current process, and returns its PID.
Typically developers do not use the spawn
functions, instead they use
abstractions such as Task
, GenServer
and Agent
, built on top of
spawn
, that spawns processes with more conveniences in terms of
introspection and debugging.
Check the Process
module for more process-related functions. For more
information on linking, check Process.link/1
.
Inlined by the compiler.
Examples
spawn_link(SomeModule, :function, [1, 2, 3])
Specs
Spawns the given function, monitors it and returns its PID and monitoring reference.
Typically developers do not use the spawn
functions, instead they use
abstractions such as Task
, GenServer
and Agent
, built on top of
spawn
, that spawns processes with more conveniences in terms of
introspection and debugging.
Check the Process
module for more process-related functions.
The anonymous function receives 0 arguments, and may return any value.
Inlined by the compiler.
Examples
current = self()
spawn_monitor(fn -> send(current, {self(), 1 + 2}) end)
Specs
Spawns the given module and function passing the given args, monitors it and returns its PID and monitoring reference.
Typically developers do not use the spawn
functions, instead they use
abstractions such as Task
, GenServer
and Agent
, built on top of
spawn
, that spawns processes with more conveniences in terms of
introspection and debugging.
Check the Process
module for more process-related functions.
Inlined by the compiler.
Examples
spawn_monitor(SomeModule, :function, [1, 2, 3])
Specs
Creates and updates structs.
The struct
argument may be an atom (which defines defstruct
)
or a struct
itself. The second argument is any Enumerable
that
emits two-element tuples (key-value pairs) during enumeration.
Keys in the Enumerable
that don't exist in the struct are automatically
discarded. Note that keys must be atoms, as only atoms are allowed when
defining a struct.
This function is useful for dynamically creating and updating structs, as
well as for converting maps to structs; in the latter case, just inserting
the appropriate :__struct__
field into the map may not be enough and
struct/2
should be used instead.
Examples
defmodule User do
defstruct name: "john"
end
struct(User)
#=> %User{name: "john"}
opts = [name: "meg"]
user = struct(User, opts)
#=> %User{name: "meg"}
struct(user, unknown: "value")
#=> %User{name: "meg"}
struct(User, %{name: "meg"})
#=> %User{name: "meg"}
# String keys are ignored
struct(User, %{"name" => "meg"})
#=> %User{name: "john"}
Specs
Similar to struct/2
but checks for key validity.
The function struct!/2
emulates the compile time behaviour
of structs. This means that:
when building a struct, as in
struct!(SomeStruct, key: :value)
, it is equivalent to%SomeStruct{key: :value}
and therefore this function will check if every given key-value belongs to the struct. If the struct is enforcing any key via@enforce_keys
, those will be enforced as well;when updating a struct, as in
struct!(%SomeStruct{}, key: :value)
, it is equivalent to%SomeStruct{struct | key: :value}
and therefore this function will check if every given key-value belongs to the struct. However, updating structs does not enforce keys, as keys are enforced only when building;
Specs
A non-local return from a function.
Check Kernel.SpecialForms.try/1
for more information.
Inlined by the compiler.
Converts the given term to a charlist according to the List.Chars
protocol.
Examples
iex> to_charlist(:foo)
'foo'
Converts the argument to a string according to the
String.Chars
protocol.
This is the function invoked when there is string interpolation.
Examples
iex> to_string(:foo)
"foo"
Provides an unless
macro.
This macro evaluates and returns the do
block passed in as the second
argument if condition
evaluates to a falsy value (false
or nil
).
Otherwise, it returns the value of the else
block if present or nil
if not.
See also if/2
.
Examples
iex> unless(Enum.empty?([]), do: "Hello")
nil
iex> unless(Enum.empty?([1, 2, 3]), do: "Hello")
"Hello"
iex> unless Enum.sum([2, 2]) == 5 do
...> "Math still works"
...> else
...> "Math is broken"
...> end
"Math still works"
Updates a nested structure via the given path
.
This is similar to update_in/3
, except the path is extracted via
a macro rather than passing a list. For example:
update_in(opts[:foo][:bar], &(&1 + 1))
Is equivalent to:
update_in(opts, [:foo, :bar], &(&1 + 1))
This also works with nested structs and the struct.path.to.value
way to specify
paths:
update_in(struct.foo.bar, &(&1 + 1))
Note that in order for this macro to work, the complete path must always
be visible by this macro. For more information about the supported path
expressions, please check get_and_update_in/2
docs.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> update_in(users["john"][:age], &(&1 + 1))
%{"john" => %{age: 28}, "meg" => %{age: 23}}
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> update_in(users["john"].age, &(&1 + 1))
%{"john" => %{age: 28}, "meg" => %{age: 23}}
Specs
Updates a key in a nested structure.
Uses the Access
module to traverse the structures
according to the given keys
, unless the key
is a
function. If the key is a function, it will be invoked
as specified in get_and_update_in/3
.
Examples
iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
iex> update_in(users, ["john", :age], &(&1 + 1))
%{"john" => %{age: 28}, "meg" => %{age: 23}}
In case any of the entries in the middle returns nil
,
an error will be raised when trying to access it next.
Uses the given module in the current context.
When calling:
use MyModule, some: :options
the __using__/1
macro from the MyModule
module is invoked with the second
argument passed to use
as its argument. Since __using__/1
is a macro, all
the usual macro rules apply, and its return value should be quoted code
that is then inserted where use/2
is called.
Examples
For example, in order to write test cases using the ExUnit
framework
provided with Elixir, a developer should use
the ExUnit.Case
module:
defmodule AssertionTest do
use ExUnit.Case, async: true
test "always pass" do
assert true
end
end
In this example, ExUnit.Case.__using__/1
is called with the keyword list
[async: true]
as its argument; use/2
translates to:
defmodule AssertionTest do
require ExUnit.Case
ExUnit.Case.__using__(async: true)
test "always pass" do
assert true
end
end
ExUnit.Case
will then define the __using__/1
macro:
defmodule ExUnit.Case do
defmacro __using__(opts) do
# do something with opts
quote do
# return some code to inject in the caller
end
end
end
Best practices
__using__/1
is typically used when there is a need to set some state (via
module attributes) or callbacks (like @before_compile
, see the documentation
for Module
for more information) into the caller.
__using__/1
may also be used to alias, require, or import functionality
from different modules:
defmodule MyModule do
defmacro __using__(_opts) do
quote do
import MyModule.Foo
import MyModule.Bar
import MyModule.Baz
alias MyModule.Repo
end
end
end
However, do not provide __using__/1
if all it does is to import,
alias or require the module itself. For example, avoid this:
defmodule MyModule do
defmacro __using__(_opts) do
quote do
import MyModule
end
end
end
In such cases, developers should instead import or alias the module
directly, so that they can customize those as they wish,
without the indirection behind use/2
.
Finally, developers should also avoid defining functions inside
the __using__/1
callback, unless those functions are the default
implementation of a previously defined @callback
or are functions
meant to be overridden (see defoverridable/1
). Even in these cases,
defining functions should be seen as a "last resort".
In case you want to provide some existing functionality to the user module,
please define it in a module which will be imported accordingly; for example,
ExUnit.Case
doesn't define the test/3
macro in the module that calls
use ExUnit.Case
, but it defines ExUnit.Case.test/3
and just imports that
into the caller when used.
When used inside quoting, marks that the given variable should not be hygienized.
The argument can be either a variable unquoted or in standard tuple form
{name, meta, context}
.
Check Kernel.SpecialForms.quote/2
for more information.
Pipe operator.
This operator introduces the expression on the left-hand side as the first argument to the function call on the right-hand side.
Examples
iex> [1, [2], 3] |> List.flatten()
[1, 2, 3]
The example above is the same as calling List.flatten([1, [2], 3])
.
The |>
operator is mostly useful when there is a desire to execute a series
of operations resembling a pipeline:
iex> [1, [2], 3] |> List.flatten() |> Enum.map(fn x -> x * 2 end)
[2, 4, 6]
In the example above, the list [1, [2], 3]
is passed as the first argument
to the List.flatten/1
function, then the flattened list is passed as the
first argument to the Enum.map/2
function which doubles each element of the
list.
In other words, the expression above simply translates to:
Enum.map(List.flatten([1, [2], 3]), fn x -> x * 2 end)
Pitfalls
There are two common pitfalls when using the pipe operator.
The first one is related to operator precedence. For example, the following expression:
String.graphemes "Hello" |> Enum.reverse
Translates to:
String.graphemes("Hello" |> Enum.reverse())
which results in an error as the Enumerable
protocol is not defined
for binaries. Adding explicit parentheses resolves the ambiguity:
String.graphemes("Hello") |> Enum.reverse()
Or, even better:
"Hello" |> String.graphemes() |> Enum.reverse()
The second pitfall is that the |>
operator works on calls.
For example, when you write:
"Hello" |> some_function()
Elixir sees the right-hand side is a function call and pipes to it. This means that, if you want to pipe to an anonymous or captured function, it must also be explicitly called.
Given the anonymous function:
fun = fn x -> IO.puts(x) end
fun.("Hello")
This won't work as it will rather try to invoke the local
function fun
:
"Hello" |> fun()
This works:
"Hello" |> fun.()
As you can see, the |>
operator retains the same semantics
as when the pipe is not used since both require the fun.(...)
notation.
Provides a short-circuit operator that evaluates and returns the second
expression only if the first one does not evaluate to a truthy value (that is,
it is either nil
or false
). Returns the first expression otherwise.
Not allowed in guard clauses.
Examples
iex> Enum.empty?([1]) || Enum.empty?([1])
false
iex> List.first([]) || true
true
iex> Enum.empty?([1]) || 1
1
iex> Enum.empty?([]) || throw(:bad)
true
Note that, unlike or/2
, this operator accepts any expression
as the first argument, not only booleans.