Is it possible to build a union type from a list? For example, something like: defmodule HatEnum do @variants [:bowler, :sombrero] # duplicated knowledge. # declare this based on @variants instead? @type t :: :bowler | :sombrero @spec name(t()) :: String.t() def name(variant) when var…

I use the following approach: # Converts a list of atoms into a typespec type = &Enum.reduce(&1, fn x, acc -> {:|, [], [x, acc]} end) @grammatical_gender [ :animate, :inanimate, :personal, :common, :feminine, :masculine, :neuter ] @type grammatical_gender :: u…

@josevalim Is it possible to do this with a macro? If not, might this be worth supporting in the language? @variants [:bowler, :sombrero] @type t :: union_type(@variants)

It’s possible. It’s not pretty. It would look something like this: requireT T.make_union_type(:t, @variants) (In another module T) defmacro make_union_type(t, a2u) do {_, atom_list@} = Code.eval_quoted(a2u, __CALLER__) {:@, [], [:type, {:::, [], [t, unroll_atoms(atoms_list)]}]} end Unro…

Oh, damn the unquote trick!! Beautiful

Elixir Programming Language Forum

Build a union type from a list?

Questions & Help Questions

freevova July 18, 2022, 6:13pm 2

It seems that no. You can check this comment.