Extract Payload for enum cases having associated value

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I think this is a problem worth solving. It's unfortunate that case name overloads complicate this so much. I'm assuming it's too late to remove support for that, but I think we'd end up with a much cleaner model if we could.

I'd prefer to take the property synthesis approach, which I think is very clean and straightforward. Due to case overloads though, doing it properly would require supporting property overloads. Which I think is reasonable given that parameterless functions can be overloaded, but it complicates getting this proposal through. I still think it's the correct approach, though.

Another option that I think would be elegant if not for case overloads is having a synthesized, nested Case enum for payload-bearing enums, which has also been discussed here before. Like this:

enum Foo {
    case bar(Int)
    case baz(String)
    
    // Synthesized:
    
    enum Case {
        case bar, baz
    }
    
    var case: Case { ... }
}

Then you can do things like foo.case == .bar, foo.payload(for: .bar), etc. It's also useful on its own -- it's not uncommon in my experience to want to refer to enum cases in general without their payloads. But this seems to be a no-go given that there's no reasonable way to synthesize the Case enum when there are case name overloads.

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