Type declarations in protocols / protocols as namespaces?

[DevAndArtist (Adrian Meister)]

Actually no. The only memory I had was that it was a reply to @anandabits and that @suyashsrijan participated in the thread. This actually helped me digging up the post I meant:

Namespacing protocols to other types

A type nested inside a generic type can be "lifted" to a top-level type whose generic arguments and requirements are the concatenation of the outer type and inner type. Eg, struct Outer<T> where T : Equatable { struct Inner<U> where U : Sequence, U.Element == T { ... } } is the same as this: struct OuterInner<T, U> where T : Equatable, U : Sequence, U.Element == T { ... } Now suppose you have a type like this: protocol Outer { struct Inner<U> where U : Sequence, U.Element == Self { ... …

I think to make the nesting work we have to provide some kind of ability to disable capturing outer generic parameters, which is why the type alias workaround already works today.