Makes the given functions in the current module overridable.

An overridable function is lazily defined, allowing a developer to override it.

Macros cannot be overridden as functions and vice-versa.

Example

defmodule DefaultMod do
  defmacro __using__(_opts) do
    quote do
      def test(x, y) do
        x + y
      end

      defoverridable test: 2
    end
  end
end

defmodule InheritMod do
  use DefaultMod

  def test(x, y) do
    x * y + super(x, y)
  end
end

As seen as in the example above, super can be used to call the default implementation.

If @behaviour has been defined, defoverridable can also be called with a module as an argument. All implemented callbacks from the behaviour above the call to defoverridable will be marked as overridable.

Example

defmodule Behaviour do
  @callback foo :: any
end

defmodule DefaultMod do
  defmacro __using__(_opts) do
    quote do
      @behaviour Behaviour

      def foo do
        "Override me"
      end

      defoverridable Behaviour
    end
  end
end

defmodule InheritMod do
  use DefaultMod

  def foo do
    "Overridden"
  end
end