perimeter_protocol.ex

defprotocol Perimeter do
  def calculate(shape)
end

defimpl Perimeter, for: Square do
  def calculate(square) do
    square.side * 4
  end
end

defimpl Perimeter, for: Circle do
  def calculate(circle)
    circle.radius * 2 * 3.14
  end
end

Perimeter.calculate(%Circle{radius: 10})
Perimeter.calculate(%Square{side: 10})