[Pitch] Opaque parameter types

[Douglas_Gregor]

@Slava_Pestov

The proposal looks great, just one small typo:

func takeStrings(_: some CollectionString>) { ... }

There's a missing < .

Fixed, thanks!

@gwendal.roue

It may be time to quote myself:

@gwendal.roue

[...] the Motivation section of the Rust RFC that accepts impl Trait (more or less our some P ) as an argument (after it was already used as a return type), is really well written. The critique rebuttals are quite interesting as well.

Yes, their motivation section is well-thought-out, and many of the arguments map precisely to Swift because Rust and Swift have very similar generics systems in this regard. It's probably worth paraphrasing their arguments and linking to that RFC, with a big disclaimed that Rust uses the term "existential" very differently, which causes endless confusion.

Doug