Hi everyone,
In prepping this proposal for review, we've encountered a snag in the implementation that will need to be addressed. Once Swift is in the OS, all new types shipped in the OS will be subject to availability via @available annotations. However, Swift does not yet have a way of annotating a conformance with availability. This is a capability that could be added to the language in future, but does not exist right now.
With new protocols, this is not a problem: the protocol itself will have availability, and therefore any conformances will too. Likewise new structs will have availability so can conform to existing protocols. But this won't apply to new conformances of existing types to existing protocols. The pitch proposes adding exactly this: of conforming existing integer types to existing ExpressibleBy... protocols.
This means we will need to adapt the proposal to accommodate this. The core team's preferred approach would be that we subset the proposal to just introducing the 'x' syntax for the scalar and grapheme literals. This addresses the pain point of having to give Character literals type context. It will also allow users to conform the integer types themselves via a short extension. Not as convenient as having it built in to the standard library, to be sure, but not too taxing. Once we have the ability to apply conformances retroactively, we could then put them in the standard library too.
Let me know your thoughts,
Ben
p.s. the ability to declare availability on a conformance is certainly something the core team expects to see added to the language in future versions of Swift – any thoughts on the design/implementation of that feature would be welcome over on the compiler development forum.