[swift-evolution] [Proposal] Enums with stored properties

[Karl]

You can already use structs as raw types. You just have to implement the RawRepresentable conformance yourself.

RawRep doesn’t affect the enum’s storage, and the shorthand syntax we’ve got saying “case a = 42” and so on is just for the compiler to synthesise a couple of switch statements. The only reason the type needs to be a string/integer literal in that case is so that we can check uniqueness and solve the most common case. If you write your own implementation, you can handle the more nuanced stuff there.

I don’t think there are any restrictions at all on RawRepresentable.RawType (not even Comparable). It can be anything you like.

Karl

> On 12 Oct 2016, at 13:22, Mateusz Malczak via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I agree, we dont event have to add a new language syntax to get this
> feature. Using structs as rawTypes would do the trick but
> 
> 1. it should be possible to use struct initializer to define enum cases
> struct MyStruct {
> var width: Int
> var height: Int
> init(width: Int, height: Int) { ... }
> }
> 
> enum MyEnum: MyStruct
> {
> case myStructCase1(width: 30, height: 30)
> case myStructCase2(width: 60, height: 60)
> ...
> }
> 
> 2. calling .rawVaue should not be required in such case to access
> stored properties
> 
> let e = MyEnum.myStructCase1
> let width = e.width // instead of e.rawValue.width
> 
> Immutability of all properties in enum struct type is already
> implemented in Swift.
> At the same time .rawValue stays as it is for primitive types.
> 
> --
> | Mateusz Malczak
> +-------------------------------
> 
> 
> 2016-10-12 13:02 GMT+02:00 J.E. Schotsman via swift-evolution
> <swift-evolution at swift.org>:
>> 
>> On 12 Oct 2016, at 09:41,Mateusz Malczak wrote:
>> 
>> 
>> That's exactly what this proposal is about. I would like to
>> keep all enum properties but add an extra feature, so that enums can
>> store some extra data.
>> 
>> 
>> If technically possible I would prefer to directly use types for enum cases.
>> Reducing a type to a tuple loses the computed properties and methods of the
>> type.
>> The types must be equatable I suppose.
>> 
>> The current enum rawValues are just indexes or keys which the compiler can
>> autogenerate (like it does for enums without a raw type).
>> Of course the raw values can be used in some smart way, like for sorting or
>> grouping cases, but this can all be done with general types - and better at
>> that.
>> 
>> So basically you have a struct type and an enum which is just a set of
>> static lets of the struct type.
>> struct MyStruct {}
>> enum MyEnum: MyStruct
>> {
>> case myStruct1
>> case myStruct2
>> ...
>> }
>> 
>> MyStruct need not be created specifically for the enum; it might be useful
>> on its own.
>> MyEnum can have additional computed properties and methods which are needed
>> for the enumerated values only.
>> 
>> The cases can be accessed like MyStruct instances. No need for .rawValue
>> except in the case of primitive types. Even there there is room for sugar
>> (if a variable is already known to be of type Int we can assign an enum:Int
>> case to it with implied .rawValue).
>> 
>> Jan E.
>> 
>> 
>> 
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution