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 fields
• name/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 list
• name/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 accepts 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.

• :includes - (a list of directories as binaries) if the record being extracted depends on relative includes, this option allows developers to specify the directory those relative includes exist

• :macros - (keyword list of macro names and values) if the record being extract 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

This function accepts 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 definitions 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 definitions to extract; with this option, this function uses the same path lookup used by the -include_lib attribute used in Erlang modules.

These options are expected to be literals (including the binary values) at compile time.

Checks if the given data is a record.

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)
true
iex> tuple = {}
iex> Record.is_record(tuple)
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