union_typespec

A simple, tiny, compile time-only library for defining an Elixir @type whose values are one of a fixed set of options.

There are two ways to use it:

1. The union_type macro, which replaces a normal @type annotation with a nice, concise macro version of the type definition.
2. UnionTypespec.union_type_ast/1, which produces an AST you can unquote within the usual @type definition.

Here's what those look like in practice:

defmodule MyModule do
  import UnionTypespec, only: [union_type: 1]

  @statuses [:read, :unread, :deleted]
  union_type status :: @statuses

  @permissions [:view, :edit, :admin]
  @type permission :: unquote(UnionTypespec.union_type_ast(@permissions))

  @spec get_permission() :: permission()
  def get_permission, do: Enum.random(@permissions)

  @spec get_status() :: status()
  def get_status, do: Enum.random(@statuses)
end

Installation

We have not yet published the package to Hex, because it's not (yet?) clear that it's valuable to anyone else. Until we do, you can still install it by adding the following to your mix.exs and running $ mix deps.get:

def deps do
  [
    {:union_typespec, git: "https://github.com/felt/union_typespec.git", tag: "v0.0.3", runtime: false},
  ]
end

And if you do find it useful, we'd love to hear about it!