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

[Karl Wagner]

Also IIRC, both of these limitations go away if you conform to RawRepresentable yourself.
  

  
There is no magic to RawRep. The compiler will just synthesise a failable initialiser and 'rawValue' computed property accessor. Both just simple switch statements matching your provided literals and returning the appropriate enum case.
  
 Specifically, RawRep does not change the raw representation of the enum. It's always going to be the smaller integer that fits the number of cases.
    
  
  
  

  
  
  
  

  
  
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> On Oct 4, 2016 at 6:56 pm,  <Karl Wagner (mailto:razielim at gmail.com)>  wrote:
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> 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.
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> 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.
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> 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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> >  _______________________________________________ swift-evolution mailing list  swift-evolution at swift.org (mailto:swift-evolution at swift.org)   https://lists.swift.org/mailman/listinfo/swift-evolution
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