I got a bit confused, I think we are here talking about completely
different features. Lets take a look at example from Karl

> enum Something {
>    case oneThing(UIView)
>    case anotherThing(Error)
>    case yetAnotherThing(Int)
> }
>
> …which is dangerously similar to Braeden’s example, really does store an 
> instance of UIView or Error or Int along with it. The size of the value is 
> the maximum of those, plus a couple of bits > to record which case it is and 
> what the type of the payload is.

This is something we already have - and example of enum with
associated values attached to enum cases. It has nothing to do with
this proposal.

The proposal is about being able to add stored immutable properties to enum type
(not to enum cases as it is in case of associated values). Just like you can
store properties in structs.

> I think he wants convenience accessors for the associated values; the
> problem is that in his example, he shouldn’t even be using associated values
> at all.

No, you are wrong, as I wrote its not even about associated values nor
about accessors.

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

I know. And this has been also already discussed. Please see a
previously discussed example here:
https://swiftlang.ng.bluemix.net/#/repl/57fbf08a4f9bcf25fdd41634

And one more example with UIView stored in enum cases
http://swiftlang.ng.bluemix.net/#/repl/57fe67ad4bb9da26d5438387

The only problem here is an amount of boilerplate code you need to
create and limitations caused by using ExpressibleBy(*)Literal.

>I agree with Karl on this. There should be clarity here as to what's proposed.
>If it's a change to how enums are laid out in memory, then you'll need to
>show we're not sacrificing performance/size in the overwhelmingly more
>common use cases, and why the extra storage is useful in the first place;
>if it's syntactic sugar, that has already been proposed multiple times and
>really isn't in scope for this phase of Swift 4--nor does it really enable any 
>new use cases not possible now.

I agree when it comes to memory and performance, but at the same time
we do not have to focus on how it should be laid out in memory. This
is already solved. It is now possible to create enumeration type with
custom structs as a rawType (see examples above). Enumeration type with
stored properties could be handled in exactly the same way. Taking
this into account I don't see any danger in terms of memory or
performance hits.

In my opinion it's also not a syntactic sugar.

Lets get back to the previously discussed example

We are discussing here a enumeration type defined as
enum RectSize
{
   let height:Int
   let width:Int
   case small(width: 30, height: 30)
   case medium(width: 60, height: 60)
   case large(width: 120, height: 120)
}
where
var size: RectSize = .small
size.height == 30 // true
size.rawValue // Error:  RectSizes has no property `rawValue`.
size.height = 40 // Error:  `height` is immutable
print(size.height) // output: 30


There are at least two ways of this could be done.

First solution would be to implement this as a new feature next to
already existing two (enum with associated values, enum with
rawValue). I don't have any detailed implementation in head.

Second approach would be to use struct as a rawValue. This feature is
already available.

struct UnderlyingRectSizeEnumStruct {
    var width: Int
    var height: Int
    init(width: width, height: height) {
        self.width = width
        self.height = height
    }
}

enum RectSize: UnderlyingRectSizeEnumStruct
{
   case small(width: 30, height: 30)
   case medium(width: 60, height: 60)
   case large(width: 120, height: 120)
}


I hope this explains what was the initial idea behind this proposal.

--
| Mateusz Malczak
+-------------------------------

2016-10-12 17:07 GMT+02:00 Karl <razie...@gmail.com>:
> Not at all - his proposal looks like the enum cases have an associated value, 
> when that is exactly what you _don’t_ want. It’s wasted storage because they 
> have a handful of known values.
>
> It’s a PITA, I get it, I go through it all the time, too; but really this is 
> the very definition of a computed property. There is nothing to be stored 
> here. Meanwhile, something like:
>
> enum Something {
>    case oneThing(UIView)
>    case anotherThing(Error)
>    case yetAnotherThing(Int)
> }
>
> …which is dangerously similar to Braeden’s example, really does store an 
> instance of UIView or Error or Int along with it. The size of the value is 
> the maximum of those, plus a couple of bits to record which case it is and 
> what the type of the payload is.
>
> Confusing those things just because you don’t like writing switch statements 
> would be bad, IMO. It’s not that much code, and once you’ve done a few of 
> them you can make it quite compact. If you have a boatload of associated 
> values, wrap them in a struct.
> Some more convenient generated accessors for the associated data might be 
> nice, but that’s been proposed and discussed to death. Others who have 
> followed the lists more closely can maybe tell you why we don’t have an 
> accepted proposal for it.
>
> - Karl
>
>> On 12 Oct 2016, at 13:52, Rien <r...@balancingrock.nl> wrote:
>>
>> I read Braeden’s example such that this proposal is in reality “just” 
>> syntactic sugar. AFAIAC it does not change how enums are implemented after 
>> compilation.
>>
>> Like sugar, it makes working with enums clearer and therefore easier. All 
>> initialisation values are defined right there with the ‘case’ instead of 
>> hidden in a tree of multiple ‘var’s.
>> While I was sceptical about this proposal, Braeden’s example makes it a +1.
>>
>> Rien.
>>
>> Btw: I made the almost identical suggestion you did ;-)
>>
>>
>>> On 12 Oct 2016, at 13:31, Karl <razie...@gmail.com> wrote:
>>>
>>> I very much disagree with the proposal, and all of the things supporting it 
>>> (like deriving enums from other types and whatnot). I think you need to 
>>> take a step up from caring about whether it’s a struct or enum and think 
>>> about what you are trying to model; that will guide you towards the correct 
>>> type(s) to use.
>>>
>>> You have only shown a handful of fixed size values, so I would suggest a 
>>> computed property in your case:
>>>
>>> enum FixedSize {
>>> case small
>>> case medium
>>> case large
>>>
>>> struct Size { let width : Int; let height: Int }
>>>
>>> var size : Size {
>>>   switch self {
>>>       case .small: return Size(width: 30, height: 30)
>>>       // … etc
>>>   }
>>> }
>>> }
>>>
>>> There is no need for these sizes to be stored at all. If you want them 
>>> baked in to your enum’s values, clearly you expect them to be specific 
>>> values. It’s more efficient to just drop the stored data altogether in this 
>>> case; this enum will get lowered in to single byte, which is more efficient 
>>> to store and transport.
>>>
>>> Karl
>>>
>>>> On 12 Oct 2016, at 13:15, Mateusz Malczak via swift-evolution 
>>>> <swift-evolution@swift.org> wrote:
>>>>
>>>>> Mateusz, you lost me with “store some extra data”.
>>>>> Does that mean something extra besides the code that Braeden suggested?
>>>>
>>>> What I meant by “store some extra data” was, to be able to define
>>>> immutable properties of any type, as a part of enum instead of
>>>> defining getters witch switches. I think Braeden example explains the
>>>> whole idea of that proposal.
>>>>
>>>> --
>>>> | Mateusz Malczak
>>>>
>>>>
>>>> 2016-10-12 8:42 GMT+02:00 Rien <r...@balancingrock.nl>:
>>>>> I’d give a +1 for the suggestion of Braeden.
>>>>>
>>>>> Mateusz, you lost me with “store some extra data”.
>>>>> Does that mean something extra besides the code that Braeden suggested?
>>>>>
>>>>> Rien.
>>>>>
>>>>>> On 12 Oct 2016, at 00:13, Mateusz Malczak via swift-evolution 
>>>>>> <swift-evolution@swift.org> 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.
>>>>>> --
>>>>>> | Mateusz Malczak
>>>>>> +-------------------------------
>>>>>> | mate...@malczak.info
>>>>>> | http://malczak.info
>>>>>>
>>>>>>
>>>>>> 2016-10-11 23:42 GMT+02:00 Braeden Profile <jhaezhy...@gmail.com>:
>>>>>>> So, just to recap, the proposed solution is to help enums expose 
>>>>>>> associated
>>>>>>> values via properties, and is not to create enums that are open to extra
>>>>>>> unnamed cases (RectSize(width:0,height:10))?  What I see is that enums 
>>>>>>> would
>>>>>>> still maintain their standing where an instance is just a selection of a
>>>>>>> finite number of options, possibly with data attached.  In proposal 1, 
>>>>>>> we
>>>>>>> want some sort of syntax where this…
>>>>>>>
>>>>>>> enum RectSize
>>>>>>> {
>>>>>>> let height:Int
>>>>>>> let width:Int
>>>>>>> case small(width: 30, height: 30)
>>>>>>> case medium(width: 60, height: 60)
>>>>>>> case large(width: 120, height: 120)
>>>>>>> }
>>>>>>>
>>>>>>> …is syntactically just like writing this…
>>>>>>>
>>>>>>> enum RectSize
>>>>>>> {
>>>>>>> case small
>>>>>>> case medium
>>>>>>> case large
>>>>>>> var height:Int
>>>>>>> {
>>>>>>>   switch self
>>>>>>>   {
>>>>>>>      case .small: return 30
>>>>>>>      case .medium: return 60
>>>>>>>      case .large: return 90
>>>>>>>   }
>>>>>>> }
>>>>>>> let width:Int
>>>>>>> {
>>>>>>>   switch self
>>>>>>>   {
>>>>>>>      case .small: return 30
>>>>>>>      case .medium: return 60
>>>>>>>      case .large: return 90
>>>>>>>   }
>>>>>>> }
>>>>>>> }
>>>>>>>
>>>>>>> …right?  That way, you can write this:
>>>>>>>
>>>>>>> var size: RectSize = .small
>>>>>>> size.height == 30 // true
>>>>>>> size.rawValue // Error:  RectSizes has no property `rawValue`.
>>>>>>> size.height = 40 // Error:  `height` is immutable
>>>>>>> size = .medium
>>>>>>>
>>>>>>> I think we were also (separately) proposing to extend `rawValue` to 
>>>>>>> take all
>>>>>>> kinds of statically known values, like structs or tuples.  Doing that 
>>>>>>> would
>>>>>>> accomplish much of the same thing.
>>>>>>>
>>>>>>> Someone fact-check me here!  I really do think something like this 
>>>>>>> would be
>>>>>>> a good idea, if we could get the right syntax.
>>>>>>>
>>>>>>> On Oct 11, 2016, at 7:06 AM, Mateusz Malczak via swift-evolution
>>>>>>> <swift-evolution@swift.org> wrote:
>>>>>>>
>>>>>>> Hi,
>>>>>>> I think we are here discussing two different aspects of introducing
>>>>>>> this new feature - code syntax and underlying implementation.
>>>>>>> In terms of code syntax I would go with first proposal as it seems to
>>>>>>> me the simplest approach. When it comes to underlying implementation,
>>>>>>> I can imagine that during compilation internal struct is created, as
>>>>>>> well as any required property getters. This way you could get a
>>>>>>> variation of rawValue implementation, at least from theoretical point
>>>>>>> of view :D
>>>>>>>
>>>>>>> --
>>>>>>> | Mateusz Malczak
>>>>>>> +-------------------------------
>>>>>>> | mate...@malczak.info
>>>>>>> | http://malczak.info
>>>>>>>
>>>>>>>
>>>>>>> 2016-10-10 23:42 GMT+02:00 Haravikk <swift-evolut...@haravikk.me>:
>>>>>>>
>>>>>>>
>>>>>>> On 10 Oct 2016, at 20:34, Mateusz Malczak <mate...@malczak.info> wrote:
>>>>>>>
>>>>>>> I know, but what I'm saying is that this problem could be solved in the
>>>>>>> multiple values case by allowing tuples as raw values for enums, since 
>>>>>>> that
>>>>>>> would allow you to specify both width and height. So it'd look something
>>>>>>> like this:
>>>>>>>
>>>>>>>
>>>>>>> We have three different possible solution
>>>>>>> 1. stored properties defined as part of enumeration type
>>>>>>> enum RectSizes: MyRect
>>>>>>> {
>>>>>>> let height:Int
>>>>>>> let width:Int
>>>>>>> case Small(width: 30, height: 30)
>>>>>>> case Medium(width: 60, height: 60)
>>>>>>> case Large(width: 120, height: 120)
>>>>>>> }
>>>>>>>
>>>>>>> 2. struct as rawValue
>>>>>>> struct MyRect
>>>>>>> {
>>>>>>> var height:Int
>>>>>>> var width:Int
>>>>>>> var area:Int {return height:Int*width}
>>>>>>> }
>>>>>>>
>>>>>>> enum RectSizes: MyRect
>>>>>>> {
>>>>>>> case Small(30,30)
>>>>>>> case Medium(60,60)
>>>>>>> case Large(120,120)
>>>>>>> }
>>>>>>>
>>>>>>> 3. tuples as rawValue
>>>>>>> enum Format : (width:Int, height:Int) {
>>>>>>> case small(30, 30)
>>>>>>> case medium(60, 60)
>>>>>>> case large(120, 120)
>>>>>>>
>>>>>>> var width:Int { return self.rawValue.width }
>>>>>>> var height:Int { return self.rawValue.height }
>>>>>>> }
>>>>>>>
>>>>>>> Solutions 2 and 3 are quire similar, to get value of a stored property
>>>>>>> we need to use rawValue or define value getters. In addition in
>>>>>>> solution 2 we define an additional data type just to be used as an
>>>>>>> enumeration type rawValue type. In my opinion, first approach would be
>>>>>>> a best solution, type definition is clear and self-explanatory because
>>>>>>> it is similar to how enums/classes are defined.
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> | Mateusz Malczak
>>>>>>>
>>>>>>>
>>>>>>> Actually I'd say your option 2 here is more similar to option 1 (you 
>>>>>>> seem to
>>>>>>> be using a struct to define the stored properties instead). The issue 
>>>>>>> here
>>>>>>> is that storing properties conflicts with what you're actually doing, 
>>>>>>> which
>>>>>>> is storing case-specific values, which is what rawValue already does, 
>>>>>>> it's
>>>>>>> just too limited for your current use-case (multiple values).
>>>>>>>
>>>>>>> The complete solution would be to introduce the concept of tuples as
>>>>>>> literals (even though they can't currently conform to types); this would
>>>>>>> make it a lot easier to support the use of any type as a fixed value for
>>>>>>> each case (not just tuples). For example, say we introduced as new 
>>>>>>> protocol:
>>>>>>>
>>>>>>> protocol ExpressableByTuple {
>>>>>>> associatedtype TupleType // somehow force this to be a tuple or
>>>>>>> ExpressableByType type
>>>>>>> init(tupleLiteral:TupleType)
>>>>>>> }
>>>>>>>
>>>>>>> With a bit of magic all tuples could conform to this protocol with
>>>>>>> themselves as the literal type, allowing us to use them as enum raw 
>>>>>>> values;
>>>>>>> likewise this could then be used to more easily enable any custom
>>>>>>> struct/class for storage in enum cases, as instead of supporting their
>>>>>>> constructors directly we can just support construction via a tuple 
>>>>>>> literal.
>>>>>>>
>>>>>>>
>>>>>>> My other reason I don't favour option 1, while it looks a bit prettier, 
>>>>>>> is
>>>>>>> that it's a bit confusing; enums have two types of stored properties, 
>>>>>>> ones
>>>>>>> that can be changed (and inspected) which is what you get when you 
>>>>>>> declare
>>>>>>> case small(Int, Int) for example, these are stored as part of the enum
>>>>>>> itself (so in that example it's 17-bytes on a 64-bit system). However
>>>>>>> rawValues are more like constants/static values, and don't increase the 
>>>>>>> size
>>>>>>> of the type, and I just feel that this is the right way to do what 
>>>>>>> you're
>>>>>>> proposing.
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> swift-evolution mailing list
>>>>>>> swift-evolution@swift.org
>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>>
>>>>>>>
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution@swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>
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>>>> swift-evolution mailing list
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>>>
>>
>
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