SE-0309: Unlock existential types for all protocols

[sighoya]

@Moximillian

With some the type is opaque to user of the function (e.g. app code using a function from a library) but it's transparent (i.e. the concrete type) to the compiler and optimizer, meaning you get the best performance from it.

Agree.

If you had read the explanation I wrote upthread, you'd know that some refers to generics,

It has a relation to them, but it isn't the same as I said upthread, at least not then anymore when they are allowed in argument type position, then the behavior differs between generics and some P.

@Moximillian

If you want to have existential, then you would need to use any P .

I disagree. But maybe the term existential is redefined in Swift context, but this would lead to more confusion for users coming from other languages already knowing existentials.