Function rustler_codegen::nif_unit_enum

pub fn nif_unit_enum(input: TokenStream) -> TokenStream

Implementation of the NifUnitEnum macro that lets the user annotate an enum with a unit type that will generate elixir atoms when encoded

#[derive(NifUnitEnum)]
enum UnitEnum {
   FooBar,
   Baz,
}

An example usage in elixir would look like the following.

test "unit enum transcoder" do
   assert :foo_bar == RustlerTest.unit_enum_echo(:foo_bar)
   assert :baz == RustlerTest.unit_enum_echo(:baz)
   assert :invalid_variant == RustlerTest.unit_enum_echo(:somethingelse)
end

Note that the :invalid_variant atom is returned if the user tries to encode something that isn't in the Rust enum.