shape_protocols_example_simple.ex

# Make some shapes
defmodule Square do
  defstruct [:side]
end

defmodule Circle do
  defstruct [:radius]
end

# define the protocol
defprotocol Shape do
  def area(shape)
end

# implement it for the Square
defimpl Shape, for: Square do
  def area(shape) do
    shape.side * shape.side
  end
end

# implement it for the Circle
defimpl Shape, for: Circle do
  def area(shape) do
    shape.radius * shape.radius * 3.14
  end
end

Shape.area(%Square{side: 10}) #=> 100
Shape.area(%Circle{radius: 10} #=> 314.0