View Source Record (Elixir v1.14.5)
Module to work with, define, and import records.
Records are simply tuples where the first element is an atom:
iex> Record.is_record({User, "john", 27})
true
This module provides conveniences for working with records at compilation time, where compile-time field names are used to manipulate the tuples, providing fast operations on top of the tuples' compact structure.
In Elixir, records are used mostly in two situations:
- to work with short, internal data
- to interface with Erlang records
The macros defrecord/3
and defrecordp/3
can be used to create records
while extract/2
and extract_all/1
can be used to extract records from
Erlang files.
Types
Types can be defined for tuples with the record/2
macro (only available in
typespecs). This macro will expand to a tuple as seen in the example below:
defmodule MyModule do
require Record
Record.defrecord(:user, name: "john", age: 25)
@type user :: record(:user, name: String.t(), age: integer)
# expands to: "@type user :: {:user, String.t(), integer}"
end
Reflection
A list of all records in a module, if any, can be retrieved by reading the
@__records__
module attribute. It returns a list of maps with the record
kind, name, tag, and fields. The attribute is only available inside the
module definition.
Link to this section Summary
Functions
Defines a set of macros to create, access, and pattern match on a record.
Same as defrecord/3
but generates private macros.
Extracts record information from an Erlang file.
Extracts all records information from an Erlang file.
Link to this section Guards
Checks if the given data
is a record.
This is implemented as a macro so it can be used in guard clauses.
Examples
Record.is_record({User, "john", 27})
#=> true
Record.is_record({})
#=> false
Checks if the given data
is a record of kind kind
.
This is implemented as a macro so it can be used in guard clauses.
Examples
iex> record = {User, "john", 27}
iex> Record.is_record(record, User)
true
Link to this section Functions
Defines a set of macros to create, access, and pattern match on a record.
The name of the generated macros will be name
(which has to be an
atom). tag
is also an atom and is used as the "tag" for the record (i.e.,
the first element of the record tuple); by default (if nil
), it's the same
as name
. kv
is a keyword list of name: default_value
fields for the
new record.
The following macros are generated:
name/0
to create a new record with default values for all fieldsname/1
to create a new record with the given fields and values, to get the zero-based index of the given field in a record or to convert the given record to a keyword listname/2
to update an existing record with the given fields and values or to access a given field in a given record
All these macros are public macros (as defined by defmacro
).
See the "Examples" section for examples on how to use these macros.
Examples
defmodule User do
require Record
Record.defrecord(:user, name: "meg", age: "25")
end
In the example above, a set of macros named user
but with different
arities will be defined to manipulate the underlying record.
# Import the module to make the user macros locally available
import User
# To create records
record = user() #=> {:user, "meg", 25}
record = user(age: 26) #=> {:user, "meg", 26}
# To get a field from the record
user(record, :name) #=> "meg"
# To update the record
user(record, age: 26) #=> {:user, "meg", 26}
# To get the zero-based index of the field in record tuple
# (index 0 is occupied by the record "tag")
user(:name) #=> 1
# Convert a record to a keyword list
user(record) #=> [name: "meg", age: 26]
The generated macros can also be used in order to pattern match on records and to bind variables during the match:
record = user() #=> {:user, "meg", 25}
user(name: name) = record
name #=> "meg"
By default, Elixir uses the record name as the first element of the tuple (the "tag").
However, a different tag can be specified when defining a record,
as in the following example, in which we use Customer
as the second argument of defrecord/3
:
defmodule User do
require Record
Record.defrecord(:user, Customer, name: nil)
end
require User
User.user() #=> {Customer, nil}
Defining extracted records with anonymous functions in the values
If a record defines an anonymous function in the default values, an
ArgumentError
will be raised. This can happen unintentionally when defining
a record after extracting it from an Erlang library that uses anonymous
functions for defaults.
Record.defrecord(:my_rec, Record.extract(...))
** (ArgumentError) invalid value for record field fun_field,
cannot escape #Function<12.90072148/2 in :erl_eval.expr/5>.
To work around this error, redefine the field with your own &M.f/a function, like so:
defmodule MyRec do
require Record
Record.defrecord(:my_rec, Record.extract(...) |> Keyword.merge(fun_field: &__MODULE__.foo/2))
def foo(bar, baz), do: IO.inspect({bar, baz})
end
Same as defrecord/3
but generates private macros.
Extracts record information from an Erlang file.
Returns a quoted expression containing the fields as a list of tuples.
name
, which is the name of the extracted record, is expected to be an atom
at compile time.
Options
This function requires one of the following options, which are exclusive to each other (i.e., only one of them can be used in the same call):
:from
- (binary representing a path to a file) path to the Erlang file that contains the record definition to extract; with this option, this function uses the same path lookup used by the-include
attribute used in Erlang modules.:from_lib
- (binary representing a path to a file) path to the Erlang file that contains the record definition to extract; with this option, this function uses the same path lookup used by the-include_lib
attribute used in Erlang modules.
It additionally accepts the following optional, non-exclusive options:
:includes
- (a list of directories as binaries) if the record being extracted depends on relative includes, this option allows developers to specify the directory where those relative includes exist.:macros
- (keyword list of macro names and values) if the record being extracted depends on the values of macros, this option allows the value of those macros to be set.
These options are expected to be literals (including the binary values) at compile time.
Examples
iex> Record.extract(:file_info, from_lib: "kernel/include/file.hrl")
[
size: :undefined,
type: :undefined,
access: :undefined,
atime: :undefined,
mtime: :undefined,
ctime: :undefined,
mode: :undefined,
links: :undefined,
major_device: :undefined,
minor_device: :undefined,
inode: :undefined,
uid: :undefined,
gid: :undefined
]
Extracts all records information from an Erlang file.
Returns a keyword list of {record_name, fields}
tuples where record_name
is the name of an extracted record and fields
is a list of {field, value}
tuples representing the fields for that record.
Options
Accepts the same options as listed for Record.extract/2
.