Elixir v1.4.5 Module View Source
Provides functions to deal with modules during compilation time.
It allows a developer to dynamically add, delete and register attributes, attach documentation and so forth.
After a module is compiled, using many of the functions in
this module will raise errors, since it is out of their scope
to inspect runtime data. Most of the runtime data can be inspected
via the __info__/1
function attached to each compiled module.
Module attributes
Each module can be decorated with one or more attributes. The following ones are currently defined by Elixir:
@after_compile
A hook that will be invoked right after the current module is compiled.
Accepts a module or a tuple {<module>, <function atom>}
.
See the “Compile callbacks” section below.
@before_compile
A hook that will be invoked before the module is compiled.
Accepts a module or a tuple {<module>, <function/macro atom>}
.
See the “Compile callbacks” section below.
@behaviour (notice the British spelling)
Behaviours can be referenced by modules to ensure they implement
required specific function signatures defined by @callback
.
For example, you can specify the URI.Parser
behaviour as follows:
defmodule URI.Parser do
@doc "Defines a default port"
@callback default_port() :: integer
@doc "Parses the given URL"
@callback parse(uri_info :: URI.t) :: URI.t
end
And then a module may use it as:
defmodule URI.HTTP do
@behaviour URI.Parser
def default_port(), do: 80
def parse(info), do: info
end
If the behaviour changes or URI.HTTP
does not implement
one of the callbacks, a warning will be raised.
@compile
Defines options for module compilation. This is used to configure both Elixir and Erlang compilers, as any other compilation pass added by external tools. For example:
defmodule M do
@compile {:inline, my_fun: 1}
def my_fun(arg) do
to_string(arg)
end
end
Multiple uses of @compile
will accumulate instead of overriding
previous ones. See the “Compile options” section below.
@doc
Provides documentation for the function or macro that follows the attribute.
Accepts a string (often a heredoc) or false
where @doc false
will
make the function/macro invisible to the documentation extraction tools
like ExDoc. For example:
defmodule M do
@doc "Hello world"
def hello do
"world"
end
@doc """
Sums `a` to `b`.
"""
def sum(a, b) do
a + b
end
end
@dialyzer
Defines warnings to request or suppress when using a version of
:dialyzer
that supports module attributes.
Accepts an atom, a tuple, or a list of atoms and tuples. For example:
defmodule M do
@dialyzer {:nowarn_function, my_fun: 1}
def my_fun(arg) do
M.not_a_function(arg)
end
end
For the list of supported warnings, see
:dialyzer
module.
Multiple uses of @dialyzer
will accumulate instead of overriding
previous ones.
@external_resource
Specifies an external resource to the current module.
Many times a module embeds information from an external file. This attribute allows the module to annotate which external resources have been used.
Tools like Mix may use this information to ensure the module is recompiled in case any of the external resources change.
@file
Changes the filename used in stacktraces for the function or macro that follows the attribute, such as:
defmodule M do
@doc "Hello world"
@file "hello.ex"
def hello do
"world"
end
end
@moduledoc
Provides documentation for the current module, such as:
defmodule M do
@moduledoc """
A very useful module
"""
end
Accepts a string (which is often a heredoc) or false
where
@moduledoc false
will make the module invisible to the
documentation extraction tools like ExDoc.
@on_definition
A hook that will be invoked when each function or macro in the current module is defined. Useful when annotating functions.
Accepts a module or a tuple {<module>, <function atom>}
. See the
“Compile callbacks” section below.
@on_load
A hook that will be invoked whenever the module is loaded.
Accepts a function atom of a function in the current module. The function
must have arity 0 (no arguments) and has to return :ok
, otherwise the
loading of the module will be aborted. For example:
defmodule M do
@on_load :load_check
def load_check do
if some_condition() do
:ok
else
:abort
end
end
def some_condition do
false
end
end
@vsn
Specify the module version. Accepts any valid Elixir value, for example:
defmodule M do
@vsn "1.0"
end
Typespec attributes
The following attributes are part of typespecs and are also reserved by Elixir:
@type
- defines a type to be used in@spec
@typep
- defines a private type to be used in@spec
@opaque
- defines an opaque type to be used in@spec
@spec
- provides a specification for a function@callback
- provides a specification for a behaviour callback@macrocallback
- provides a specification for a macro behaviour callback@optional_callbacks
- specifies which behaviour callbacks and macro behaviour callbacks are optional
Custom attributes
In addition to the built-in attributes outlined above, custom attributes may
also be added. A custom attribute is any valid identifier prefixed with an
@
and followed by a valid Elixir value:
defmodule M do
@custom_attr [some: "stuff"]
end
For more advanced options available when defining custom attributes, see
register_attribute/3
.
Compile callbacks
There are three callbacks that are invoked when functions are defined, as well as before and immediately after the module bytecode is generated.
@after_compile
A hook that will be invoked right after the current module is compiled.
Accepts a module or a tuple {<module>, <function atom>}
. The function
must take two arguments: the module environment and its bytecode.
When just a module is provided, the function is assumed to be
__after_compile__/2
.
Example
defmodule M do
@after_compile __MODULE__
def __after_compile__(env, _bytecode) do
IO.inspect env
end
end
@before_compile
A hook that will be invoked before the module is compiled.
Accepts a module or a tuple {<module>, <function/macro atom>}
. The
function/macro must take one argument: the module environment. If it’s a
macro, its returned value will be injected at the end of the module definition
before the compilation starts.
When just a module is provided, the function/macro is assumed to be
__before_compile__/1
.
Note: unlike @after_compile
, the callback function/macro must
be placed in a separate module (because when the callback is invoked,
the current module does not yet exist).
Example
defmodule A do
defmacro __before_compile__(_env) do
quote do
def hello, do: "world"
end
end
end
defmodule B do
@before_compile A
end
@on_definition
A hook that will be invoked when each function or macro in the current module is defined. Useful when annotating functions.
Accepts a module or a tuple {<module>, <function atom>}
. The function
must take 6 arguments:
- the module environment
- kind:
:def
,:defp
,:defmacro
, or:defmacrop
- function/macro name
- list of quoted arguments
- list of quoted guards
- quoted function body
Note the hook receives the quoted arguments and it is invoked before
the function is stored in the module. So Module.defines?/2
will return
false
for the first clause of every function.
If the function/macro being defined has multiple clauses, the hook will be called for each clause.
Unlike other hooks, @on_definition
will only invoke functions
and never macros. This is because the hook is invoked inside the context
of the function (and nested function definitions are not allowed in
Elixir).
When just a module is provided, the function is assumed to be
__on_definition__/6
.
Example
defmodule H do
def on_def(_env, kind, name, args, guards, body) do
IO.puts "Defining #{kind} named #{name} with args:"
IO.inspect args
IO.puts "and guards"
IO.inspect guards
IO.puts "and body"
IO.puts Macro.to_string(body)
end
end
defmodule M do
@on_definition {H, :on_def}
def hello(arg) when is_binary(arg) or is_list(arg) do
"Hello" <> to_string(arg)
end
def hello(_) do
:ok
end
end
Compile options
The @compile
attribute accepts diverse options that is used by both
Elixir and Erlang compilers. Some of the common use cases are documented
below:
@compile :debug_info
- includes:debug_info
regardless of the setting inCode.compiler_options/1
@compile {:debug_info, false}
- disables:debug_info
regardless of the setting inCode.compiler_options/1
@compile {:inline, some_fun: 2, other_fun: 3}
- inlines the given name/arity pairs@compile {:autoload, false}
- disables automatic loading of modules after compilation. Instead, the module will be loaded after it is dispatched to
You can see a handful more options used by the Erlang compiler in
the documentation for the :compile
module.
Link to this section Summary
Functions
Provides runtime information about functions and macros defined by the module, enables docstring extraction, etc
Attaches documentation to a given function or type
Concatenates a list of aliases and returns a new alias
Concatenates two aliases and returns a new alias
Creates a module with the given name and defined by the given quoted expressions
Checks if the module defines the given function or macro
Checks if the module defines a function or macro of the
given kind
Returns all functions defined in module
Returns all functions defined in module
, according
to its kind
Deletes the module attribute that matches the given key
Evaluates the quoted contents in the given module’s context
Gets the given attribute from a module
Makes the given functions in module
overridable
Checks if a module is open, i.e. it is currently being defined and its attributes and functions can be modified
Returns true
if tuple
in module
is marked as overridable
Puts a module attribute with key and value in the given module
Registers an attribute
Concatenates a list of aliases and returns a new alias only if the alias was already referenced
Concatenates two aliases and returns a new alias only if the alias was already referenced
Splits the given module name into binary parts
Link to this section Functions
__info__(:attributes | :compile | :exports | :functions | :macros | :md5 | :module | :native_addresses) :: atom | [{atom, any} | {atom, byte, integer}]
Provides runtime information about functions and macros defined by the module, enables docstring extraction, etc.
Each module gets an __info__/1
function when it’s compiled. The function
takes one of the following atoms:
:functions
- keyword list of public functions along with their arities:macros
- keyword list of public macros along with their arities:module
- module name (Module == Module.__info__(:module)
)
In addition to the above, you may also pass to __info__/1
any atom supported
by :erlang.module_info/0
which also gets defined for each compiled module.
For a list of supported attributes and more information, see Modules – Erlang Reference Manual.
Attaches documentation to a given function or type.
It expects the module the function/type belongs to, the line (a non
negative integer), the kind (def
or defmacro
), a tuple representing
the function and its arity, the function signature (the signature
should be omitted for types) and the documentation, which should
be either a binary or a boolean.
Examples
defmodule MyModule do
Module.add_doc(__MODULE__, __ENV__.line + 1, :def, {:version, 0}, [], "Manually added docs")
def version, do: 1
end
Concatenates a list of aliases and returns a new alias.
Examples
iex> Module.concat([Foo, Bar])
Foo.Bar
iex> Module.concat([Foo, "Bar"])
Foo.Bar
Concatenates two aliases and returns a new alias.
Examples
iex> Module.concat(Foo, Bar)
Foo.Bar
iex> Module.concat(Foo, "Bar")
Foo.Bar
Creates a module with the given name and defined by the given quoted expressions.
The line where the module is defined and its file must be passed as options.
Examples
contents =
quote do
def world, do: true
end
Module.create(Hello, contents, Macro.Env.location(__ENV__))
Hello.world #=> true
Differences from defmodule
Module.create/3
works similarly to defmodule
and
return the same results. While one could also use
defmodule
to define modules dynamically, this
function is preferred when the module body is given
by a quoted expression.
Another important distinction is that Module.create/3
allows you to control the environment variables used
when defining the module, while defmodule
automatically
shares the same environment.
Checks if the module defines the given function or macro.
Use defines?/3
to assert for a specific type.
Examples
defmodule Example do
Module.defines? __MODULE__, {:version, 0} #=> false
def version, do: 1
Module.defines? __MODULE__, {:version, 0} #=> true
end
Checks if the module defines a function or macro of the
given kind
.
kind
can be any of :def
, :defp
, :defmacro
or :defmacrop
.
Examples
defmodule Example do
Module.defines? __MODULE__, {:version, 0}, :defp #=> false
def version, do: 1
Module.defines? __MODULE__, {:version, 0}, :defp #=> false
end
Returns all functions defined in module
.
Examples
defmodule Example do
def version, do: 1
Module.definitions_in __MODULE__ #=> [{:version, 0}]
end
Returns all functions defined in module
, according
to its kind.
Examples
defmodule Example do
def version, do: 1
Module.definitions_in __MODULE__, :def #=> [{:version, 0}]
Module.definitions_in __MODULE__, :defp #=> []
end
delete_attribute(module, key :: atom) :: value :: term
Deletes the module attribute that matches the given key.
It returns the deleted attribute value (or nil
if nothing was set).
Examples
defmodule MyModule do
Module.put_attribute __MODULE__, :custom_threshold_for_lib, 10
Module.delete_attribute __MODULE__, :custom_threshold_for_lib
end
Evaluates the quoted contents in the given module’s context.
A list of environment options can also be given as argument.
See Code.eval_string/3
for more information.
Raises an error if the module was already compiled.
Examples
defmodule Foo do
contents = quote do: (def sum(a, b), do: a + b)
Module.eval_quoted __MODULE__, contents
end
Foo.sum(1, 2) #=> 3
For convenience, you can pass any Macro.Env
struct, such
as __ENV__/0
, as the first argument or as options. Both
the module and all options will be automatically extracted
from the environment:
defmodule Foo do
contents = quote do: (def sum(a, b), do: a + b)
Module.eval_quoted __ENV__, contents
end
Foo.sum(1, 2) #=> 3
Note that if you pass a Macro.Env
struct as first argument
while also passing opts
, they will be merged with opts
having precedence.
Gets the given attribute from a module.
If the attribute was marked with accumulate
with
Module.register_attribute/3
, a list is always returned.
nil
is returned if the attribute has not been marked with
accumulate
and has not been set to any value.
The @
macro compiles to a call to this function. For example,
the following code:
@foo
Expands to something akin to:
Module.get_attribute(__MODULE__, :foo)
Examples
defmodule Foo do
Module.put_attribute __MODULE__, :value, 1
Module.get_attribute __MODULE__, :value #=> 1
Module.register_attribute __MODULE__, :value, accumulate: true
Module.put_attribute __MODULE__, :value, 1
Module.get_attribute __MODULE__, :value #=> [1]
end
Makes the given functions in module
overridable.
An overridable function is lazily defined, allowing a
developer to customize it. See Kernel.defoverridable/1
for
more information and documentation.
Checks if a module is open, i.e. it is currently being defined and its attributes and functions can be modified.
Returns true
if tuple
in module
is marked as overridable.
put_attribute(module, key :: atom, value :: term) :: :ok
Puts a module attribute with key and value in the given module.
Examples
defmodule MyModule do
Module.put_attribute __MODULE__, :custom_threshold_for_lib, 10
end
Registers an attribute.
By registering an attribute, a developer is able to customize how Elixir will store and accumulate the attribute values.
Options
When registering an attribute, two options can be given:
:accumulate
- several calls to the same attribute will accumulate instead of override the previous one. New attributes are always added to the top of the accumulated list.:persist
- the attribute will be persisted in the Erlang Abstract Format. Useful when interfacing with Erlang libraries.
By default, both options are false
.
Examples
defmodule MyModule do
Module.register_attribute __MODULE__,
:custom_threshold_for_lib,
accumulate: true, persist: false
@custom_threshold_for_lib 10
@custom_threshold_for_lib 20
@custom_threshold_for_lib #=> [20, 10]
end
safe_concat([binary | atom]) :: atom | no_return
Concatenates a list of aliases and returns a new alias only if the alias was already referenced.
If the alias was not referenced yet, fails with ArgumentError
.
It handles charlists, binaries and atoms.
Examples
iex> Module.safe_concat([Module, Unknown])
** (ArgumentError) argument error
iex> Module.safe_concat([List, Chars])
List.Chars
safe_concat(binary | atom, binary | atom) :: atom | no_return
Concatenates two aliases and returns a new alias only if the alias was already referenced.
If the alias was not referenced yet, fails with ArgumentError
.
It handles charlists, binaries and atoms.
Examples
iex> Module.safe_concat(Module, Unknown)
** (ArgumentError) argument error
iex> Module.safe_concat(List, Chars)
List.Chars