Can the compiler be more helpful when we need to explicitly, dynamically specialize existentials?

Evolution Discussion
18

I think if case fits well once you get used to it. I have several complaints, however:

  • When you type the if case let statement, the sourcekit is not able to make an autocomplete suggestion, as it does with switch case, because the variable you want to match is typed last. One solution from my point of view, would be to allow the matched variable on left side, like this:
enum A { case a(Int), b(Int) }

let a = A.a(1); let b = A.b(2)

if a = case let .a(anInt), case let .b(anInt2) = b { print(anInt + anInt2) }
// or 
if case a = let .a(anInt), case let .b(anInt2) = b { print(anInt + anInt2) }
// or even requirement to use pattern mathing operator would be fine fmpov
if a ~= let .a(anInt), case let .b(anInt2) = b { print(anInt + anInt2) }
  • The other factor that makes me less enthusiastic about enums (again, fmpov) is, that In-place mutation of an enum associated value is still not possible. If this was possible, enums would get huge advantage over any "sealed" protocol based solution.