Question/proposal: Struct specialization

[Pscheidl]

Question/proposal: Struct specialization

[kennytm]

You don't need dynamic dispatch.

#![feature(specialization)]

trait Lookup: Sized {
    type Collection: Collection<Self>;
}

impl<T> Lookup for T {
    default type Collection = Vec<T>;
}

impl<T: Hash> Lookup for T {
    type Collection = HashSet<T>;
}

struct Wrapper<T: Lookup> {
    information: T::Collection,
}

[Pscheidl]

True, thank you. Doable once (if) Impl specialization arives then. It is quite verbose, but I can see the advantage of that. On the other hand, the approach ^ could be treated as a syntactic sugar ?

[kennytm]

the approach ^ could be treated as a syntactic sugar ?

At least the syntax proposed in OP is impossible, since without a concrete T you don't know the exact type of self.information and thus can't call any useful method. You still need that Collection trait and with that struct specialization syntax you can't associate the trait Collection to the member information anywhere.