I’m still fairly new to the language. I wanted to know more about the “Elixir” way of doing things so I wrote a tiny program 3 ways, but I’m not sure which is the “right way”. I know you’d normally want only one module per page, this is just for demonstration purposes.

This one has the most isoloation of responsibilities:

defmodule Shapes do
  defmodule Rectangle do
    defstruct [:width, :height]

    def perimeter(%Rectangle{width: width, height: height}) do
      2 * (width + height)
    end

    def area(%Rectangle{width: width, height: height}) do
      width * height
    end
  end

  defmodule Circle do
    defstruct [:radius]

    def area(%Circle{radius: radius}) do
      radius * radius * :math.pi()
    end
  end
end

This one leverages pattern matching a little more.

defmodule Shape do
  defmodule Rectangle do
    defstruct [:width, :height]
  end

  defmodule Circle do
    defstruct [:radius]
  end

  def perimeter(%Rectangle{width: width, height: height}) do
    2 * (width + height)
  end

  def area(%Rectangle{width: width, height: height}) do
    width * height
  end

  def area(%Circle{radius: radius}) do
    radius * radius * :math.pi()
  end
end

This is my attempt at implementing it as a protocol. I’m a little unsure
because to my understanding protocols are for taking in different types.

defprotocol Shape do
  def area(data)
  def perimeter(data)
end

defmodule Rectangle do
  defstruct [:width, :height]

  defimpl Shape, for: Rectangle do
    def area(%Rectangle{width: width, height: height}) do
      width * height
    end

    def perimeter(%Rectangle{width: width, height: height}) do
      2 * (width + height)
    end
  end
end

defmodule Circle do
  defstruct [:radius]

  defimpl Shape, for: Circle do
    def area(%Circle{radius: radius}) do
      :math.pi() * radius * radius
    end
  end
end

Thank you for any help