Programming Elixir 1.2

Built-In Protocols

Elixir comes with the following protocols:

• Enumerable and Collectable
• Inspect
• List.Chars
• String.Chars

To play with these, we’ll implement a trivial datatype that represents the collection of 0s and 1s in an integer. The underlying representation is trivial:

protocols/bitmap.exs

defmodule Bitmap do
  defstruct value: 0

  @doc """
  A simple accessor for the 2^bit value in an integer

      iex> b = %Bitmap{value: 5}
      %Bitmap{value: 5}
      iex> Bitmap.fetch_bit(b,2)
      1
      iex> Bitmap.fetch_bit(b,1)
      0
      iex> Bitmap.fetch_bit(b,0)
      1
  """
  def fetch_bit(%Bitmap{value: value}, bit) do
    use Bitwise

    (value >>> bit) &&& 1
  end
end

The fetch_bit function uses the >>> and &&& functions in ...