Adzz

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

Adzz

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

Adzz

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

Adzz

defmodule EquilateralTriangle do
  defstruct [:side]
end

Adzz

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

defmodule Circle do
  defstruct [:radius]
end

defmodule EquilateralTriangle do
  defstruct [:side]

Adzz

class Square
  def initialize(side)
     @side = side
  end

  def area()
    @side * @side
  end
end

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class Circle
  def initialize(radius)
    @radius = radius
  end
  
  def area()
    3.14 * @radius * @radius
  end
end

Adzz

defmodule Square do
  defstruct [:side]
end

defmodule Circle do
  defstruct [:radius]
end

defmodule Area do
  def calculate(shape) do