A protocol that builds a string to converts into a slug

This protocol is used by Slugy.slugify/2. For example, when you want a custom slug for a Post, composed by the title and the published_at fields:

"how-to-use-slugy-2018-10-10"

Suppose you have a Post module with the following fields:

defmodule Post do
  schema "posts" do
    field :title, :string
    field :body, :text
    field :published_at, :datetime
  end
end

You need to implement the Slugy.Slug protocol to achieve that:

defimpl Slugy.Slug, for: Post do
  def to_slug(%{title: title, published_at: published_at}) do
    "#{title} #{published_at}"
  end
end

Slugy internally uses this string to build your custom slug.