[swift-evolution] [Pitch] Hashable types on RawRepresentable enums or a protocol for custom enum-like types

[Karl Wagner]

Enum raw types don't have to be strings/integers, but they have to be expressable by string or integer literals.   We don't guarantee uniqueness per se, but we do check for duplicate literals and auto-increment integers to fill gaps.
  
  

  
  
  
  

  
So all you have to do is make your custom type conform to ExpressibleByStringLiteral and you can use it as an enum's raw type.
  

  
Karl
  
  
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> On Oct 3, 2016 at 9:50 pm,  <Adrian Zubarev via swift-evolution (mailto:swift-evolution at swift.org)>  wrote:
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> Hi there,
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> I’m interested if this idea has some potential future in Swift or not.
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> Currently RawRepresentable enums accept only a subset of literal types like String, Character and the Integer family (enum Name : String { … }).
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> Sometimes this is not enough for my use-case and I wish I could feed my enums with other Hashable types!
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> As a workaround I can create a custom struct or even a class and conform it to  RawRepresentable  and fake an enum with some static variables (similar to what is done with  OptionSet  types).
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> The problem there is that I cannot use the same switch pattern matching like with enums. I’d wish either enums could accept Hashable types (maybe with some restriction) or the existence on a protocol to build custom enum-like types with strucs/classes and use the same switch pattern matching.
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>   struct A : Hashable { /* implement everything */ } // Variant 1: enum Test : A { case something = A(rawValue: A(value: "something")) case nothing = A(rawValue: A(value: "nothing")) } // Variant 2: protocol SomeFancyName : RawRepresentable { … } struct Test : SomeFancyName { let rawValue: A init?(rawValue: A) { // Implement + reject unwanted `A`s } static let something = A(rawValue: A(value: "something")) static let nothing = A(rawValue: A(value: "nothing")) } let value = Test.something switch value { case .something: // handle case .nothing: // handle // Because of `SomeFancyName` the switch can use enum-like pattern matching + does not need the `default` case when all cases are present }    
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>  --   
>  Adrian Zubarev
>  Sent with Airmail       
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