Macro one_way_slot_map::define_key_type

macro_rules! define_key_type {
    ($key_type:ident<$pointer_type:ty> $(: $derive_1:ident $(+ $more_derives:ident)* )?) => { ... };
}

Macro for creating a simple Key type for one-way slot maps. Key types can be created from scratch, but for most cases, this will produce what you want