Directive to exclude struct fields from being using'd

[mr0x13f]

I ran into the situation where I had a struct that was using two other structs, which both have fields with the same name. I didn't really want to use #subtype instead, as I do want to pull some fields into the parent struct's namespace.
A solution to this could be to add a new directive that is put in front of struct fields, which causes them to be excluded from being pulled into the namespace when using the struct. Let's call it #hidden for now.

Example:

Entity :: struct {
   using trait_a: Trait_A,
   using trait_b: Trait_B, 
   some_entity_field: u8,
}

Trait_A :: struct {
   #hidden using entity: ^Entity, 
   some_trait_field: u8,
}

Trait_B :: struct {
   #hidden using entity: ^Entity,
   some_other_trait_field: u8,
}

Here the Entity struct pulls in fields from Trait_A and Trait_B. These traits themself have a using'd pointer back to the parent Entity, which enables both 'up-casting' Entity to a trait and 'down-casting' a trait back to the Entity.
Note that in this example I've put the directive on a field that's also using, but non-using fields could work the same.
A 'hidden' field could of course still be accessed explicitly, i.e.: entity.trait_a.entity.

Without the new directive, the pointers to Entity would all need unique names, even though it's a field that doesn't really need to be pulled into the namespace anyway. Otherwise the traits can't be using'd by Entity.

[gingerBill]

There is #subtype if you want the subtyping behaviour but not the using namespace aspect.