Adzz

defmodule Project do
  def total_cost(shape, cost_per_square_meter) do
    Shape.area(shape) * cost_per_square_meter
  end
end

Adzz

defimpl Shape, for: EquilateralTriangle do
  def area(shape) do
    # some basic high school math that I've forgotten
  end
end

Adzz

defmodule EquilateralTriangle do
  defstruct [:side]
end

Adzz

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

Adzz

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

Adzz

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

Adzz

defprotocol Shape do
  def area(shape)
end

Adzz

defmodule Project do
  def total_cost(shape, cost_per_square_meter) do
      Shape.area(shape) * cost_per_square_meter
  end
end

Adzz

defmodule Project do
  def total_cost(shape = %Square{}, cost_per_square_meter) do
      Square.area(shape) * cost_per_square_meter
  end
  def total_cost(shape = %Circle{}, cost_per_square_meter) do
    Circle.area(shape) * cost_per_square_meter
  end
end

Adzz

defmodule Project do
  def total_cost(shape, cost_per_square_meter) do
    case shape do
      %Square{} -> Square.area(shape) * cost_per_square_meter
      %Circle{} -> Circle.area(shape) * cost_per_square_meter
    end
  end
end