Extract Payload for enum cases having associated value

Evolution Pitches
,
239

If it were up to me, I'd overhaul enums completely. The model I want is this:

  enum MyEnum {
     case 
          foo(label:String, Int),
          bar(Double),
          baz
  }

Usage

  let 
     a: MyEnum = .bar(123.0),
     cpy: MyEnum = a, // .bar(123.0) case and its payload
     val: Double = a() // 123.0 payload only

  let 
     b: MyEnum = .bar(123.0),
     c: MyEnum = .bar(456.0),
     d: MyEnum = .baz

   a == b // true (both are 'bar')
   a === b // true (both 'bar' and same payload)

   a == c // true
   a === c // false  (different payload)

   a == b // false
   a === b // false

I have essentially been using this model (via structs), and it works well. The trouble with using a struct is that the declaration of the struct involves a lot of code repetition (you have to declare both a static var and a static function overloaded with the same name for every 'case') and wasted storage for the backing id. Also, if it were built-in, Swift could warn you, when you, for example, try to compare two cases with payloads of different types.