• A map to strore the data
• it’s like a map but has two advantages.
  • The only thing I can put on struct is what I defined.
• It can not store any method (different to class), so it’s right under the map but with some constraints.

defmodule Identicon.Image do
	defstruct hex: nil
end

%Identicon.Image{}
# it looks like a map, and it has the default keys (i.e. hex)
# And you can only add the registered keys.

Pattern matching Struct

• Goal: to get the first three elements of list from struct

defmodule Identicon do
	def main(input) do
		input
		|> hash_input
		|> pick_color
	end

	def pick_color(image) do
		# red = image.hexa[0] # this sort of array accessing doesn't work in elixir.
		%Identicon.Image{hex: hex_list} = image # pattern matching! pull of the list
		# [r, g, b] = hex_list # doesn't work because much more hex numbers than 3		
		[r, g, b | _tail] = hex_list # _ means I don't care the remainder.

		# if I put them in one line,
		%Identicon.Image{hex: [r,g,b | _tail} = image 
	end

	def hash_input(input) do
		hex = :crypto.hash(:md5, input)
		|> :binary.bin_to_list

		%Identicon.Image{hex: hex}
	end
end

Updating struct

defmodule Identicon.Image do
	defstruct hex: nil, color: nil
end

defmodule Identicon do
	def main(input) do
		input
		|> hash_input
		|> pick_color
	end

	def pick_color(image) do
		%Identicon.Image{hex: [r,g,b | _tail} = image 
		
		# image.color = {r,g,b} # don't do! it's js-script way
		%Identicon.Image{image | color: {r, g, b}}
		# Make a new struct taking all existing struct (image) and update (color)
	end

#### Same function, but it uses the pattern matching of argument)
	def pick_color(%Identicon.Image{hex: [r,g,b | _tail} = image ) do
		%Identicon.Image{image | color: {r, g, b}}
	end

	def hash_input(input) do
		hex = :crypto.hash(:md5, input)
		|> :binary.bin_to_list

		%Identicon.Image{hex: hex}
	end
end