elixir-protocols.ex

defprotocol Area do
  @doc "Calculate the area for a given object"
  def area(object)
end

defimpl Area, for: Rectangle do
  def area(rectangle) do
    rectangle.width * rectangle.length
  end
end

defimpl Area, for: Circle do
  def area(circle) do
    :math.pow(circle.radius * :math.pi, 2)
  end
end

# These are arbritrary shape structs, but ignoring that fact, 
# we have defined a protocol and a couple of implementations. 
# Usage is then as easy as:

iex> Area.area(%Rectangle{width: 5, length: 3})
15

iex> Area.area(%Circle{radius: 5})
246.74011002723395

:math.pow(circle.radius, 2) * :math.pi