[swift-evolution] Fixing raw enum types

[Goffredo Marocchi]

Now is still the time for source breaking changes if well motivated, when dealing with key aspects of the language and we can make them objectively better then we ought to act when we can I think.

+1

Sent from my iPhone

> On 17 Jan 2017, at 06:11, Pranshu Goyal via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Definitely a +1, this clarifies intent, but enums are used a lot in swift code, and considering this is a source breaking change I'm not sure if many users of swift are going to be positive about this.
> 
>> On 17 January 2017 at 02:32, David Waite via swift-evolution <swift-evolution at swift.org> wrote:
>> Or perhaps paint the bikeshed 
>> 
>> enum Something<(Int32, Int32)> { … }
>> 
>> -DW
>>> On Jan 16, 2017, at 11:51 AM, Anton Zhilin via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> This idea by Karl made me branch off a new thread.
>>> 
>>> 2017-01-16 21:28 GMT+03:00 Karl Wagner <razielim at gmail.com>:
>>> 
>>> 
>>> 
>>>> It would be helpful for synthesised RawRep conformance. The inheritance-like syntax we have now is awful - it makes people think that RawRepresentable is some kind of magic protocol that will allow special compiler jango to happen.
>>>> 
>>>> You could see why they think that. This looks very much like the enum is going to *be* an Int32:
>>>> 
>>>> enum Something: Int32 {
>>>>     case oneThing = 36
>>>>     case anotherThing = 42
>>>> }
>>>> 
>>>> This is also one of the icky parts to allowing tuples of integer/string literals (something people ask for quite a lot). It would look like you’re deriving your enum from a non-nominal type:
>>>> 
>>>> enum Something: (Int32, Int32) {
>>>>     case oneThing = (3, 12)
>>>>     case anotherThing = (5, 9)
>>>> }
>>> 
>>> 
>>> Even if Swift gains newtype, it’s not that case. The enum does not gain methods or behavior of the specified type. It’s just a shorthand, hinting the compiler to provide correct RawRepresentable conformance.
>>> 
>>> I suggest to invent a new syntax for this type hinting for RawRepresentable. For example, it can be an annotation:
>>> 
>>> @raw(Int32) enum Something {
>>>     // ...
>>> }
>>> Or a contextual keyword:
>>> 
>>> enum Something : raw(Int32) {
>>>     // ...
>>> }
>>> Perhaps, he most uniform and explicit of syntaxes:
>>> 
>>> enum Something : RawRepresentable {
>>>     case oneThing = 36
>>>     case anotherThing = 42
>>> }
>>> 
>>> enum AnotherThing : RawRepresentable {
>>>     typealias RawValue = Int32
>>>     case oneThing
>>>     case anotherThing
>>> }
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>> 
>> 
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> 
> 
> 
> -- 
> Pranshu Goyal
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