Typecasting for `some`

[Jumhyn (Frederick Kellison-Linn)]

That's never been forced except for protocols with associated types which couldn't previously be written with the 'bare' protocol name syntax. The upcoming feature flag which would have enforced this for all protocols in the Swift 6 language mode was deferred to a future language version:

@hborla

The Language Steering Group has decided that one previously-accepted upcoming feature, ExistentialAny, will not be enabled by default in Swift 6. SE-0335: Introduce existential any introduces the any keyword to identify existential types. The proposal also specifies that "bare" protocol names will no longer be permitted as types---they must either use any or some, as appropriate---under the upcoming feature flag ExistentialAny. Given the concerns about migration to consistent use of existential any in the language, and the expectation that additional language improvements will be coming that might affect the end result of that migration, the Language Steering Group is deferring the source-incompatible changes in SE-0335 to a future language revision.