Programming Elixir 1.3

Defining New Types

The attribute @type can be used to define new types.

@type type_name :: type_specification

Elixir uses this to predefine some built-in types and aliases.

@type term      :: any
@type binary    :: <<_::_*8>>
@type bitstring :: <<_::_*1>>
@type boolean   :: false | true
@type byte      :: 0..255
@type char      :: 0..0x10ffff
@type list      :: [ any ]
@type list(t)   :: [ t ]
@type number    :: integer | float
@type module    :: atom
@type mfa       :: {module, atom, byte}
@type node      :: atom
@type timeout   :: :infinity | non_neg_integer
@type no_return :: none

As the list(t) entry shows, you can parameterize the types in a new definition. Simply use one or more identifiers as parameters on the left side, and use these identifiers where you’d otherwise ...