Utilities for defining behaviour interfaces.

Behaviours can be referenced by other modules to ensure they implement required callbacks.

For example, you can specify the URI.Parser behaviour as follows:

defmodule URI.Parser do
  use Behaviour

  @doc "Parses the given URL"
  defcallback parse(uri_info :: URI.t) :: URI.t

  @doc "Defines a default port"
  defcallback default_port() :: integer
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.

Implementation

Since Erlang R15, behaviours must be defined via @callback attributes. defcallback is a simple mechanism that defines the @callback attribute according to the given type specification. defcallback allows documentation to be created for the callback and defines a custom function signature.

The callbacks and their documentation can be retrieved via the __behaviour__ callback function.