Programmer Passport: Elixir

Structs Are Restricted Maps

A struct is a specific kind of map. Where a map can have any combination of keys, every struct that conforms to a type has a specific list of keys.

Structs are ideal for holding metadata for a type. Let’s put structs into practice to build an SVG graphic.

We’re going to create an SVG graphic representation that we’ll eventually put in a text file that looks like this:

<svg viewBox="0 0 200 200" xmlns="http://www.w3.org/2000/svg">
  <polygon points="100,100 150,25 150,75 200,0"
            fill="none" stroke="black" />
</svg>

defstruct Defines a Struct

Let’s switch back to our graphics project. Open up a file called shape.ex and key this in:

defmodule Shape do
  defstruct([:points, :stroke, :fill])
end

We’ve defined ...