[Pitch] Primary Associated Types in the Standard Library

[lorentey (Karoy Lorentey)]

@sjavora

I'd like to echo a concern from @Karl from the review thread - some Identifiable<Int> reads like "identifiable int"... which is not what this is.

@xwu

This would apply to Strideable as well, though, and more broadly to any *able (and *ing ) protocol (since the "-able" always refers to an ability of Self and the primary associated type would never be Self ).

I 100% get this, but on the other hand, this is an inherent trade off in this feature -- we don't have labels for things within angle brackets, so it isn't at all obvious what Int means in MyProtocol<Int> or MyGenericStruct<Int>. To understand these, I have to go look at the declaration/documentation of the protocol/struct.

(Incidentally, the first cut of SE-0346 highlighted that we don't have a formal way to add API docs for type parameters of a generic type or generic function.)

If we were to take this objection seriously, then that would effectively mean that SE-0346 will be strictly limited to Sequence-style container protocols. Then again, I'm sure even Collection<Int> will confuse somebody: is it providing a collection interface to access individual bits in an integer?

My impression from reading the Core Team's verdict is that this is intended to be a general-purpose alternative to the classic generic declaration syntax, not some niche feature that is dedicated to sequences.