Derive Macro rustler_codegen::NifUnitEnum

#[derive(NifUnitEnum)]
{
    // Attributes available to this derive:
    #[rustler]
}

Derives implementations for the Encoder and Decoder traits which convert between an enum and a union of elixir atoms.

For example:

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

Then the traits Encoder and Decoder are derived automatically for your Rust struct such that FooBar is encoded to, and decoded from, :foo_bar.

• The variant name is translated from camel case to snake case for the atom name.
• Each constructor is required not to have arguments, i.e. to be of unit type.

An example usage in Rust and Elixir would look like the following.

#[rustler::nif]
pub fn unit_enum_echo(unit_enum: UnitEnum) -> UnitEnum {
    unit_enum
}

(We are leaving out some boiler plate code to connect the rust code to elixir functions.)

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