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

[Mateusz Malczak]

> Is this what you're trying to achieve, only using a nicer syntax to
> represent it?
> http://swiftlang.ng.bluemix.net/#/repl/57fb8ac27365890cc848f831

Yes
This similar to example shown in my original email, where struct is
used as a rawType and custom string literal parsing to assign values
to enum cases.
http://swiftlang.ng.bluemix.net/#/repl/57fb8e3e4f9bcf25fdd415cd

What I would like to achieve is (more or less)
http://swiftlang.ng.bluemix.net/#/repl/57fb98074f9bcf25fdd415d8

regards
--
| Mateusz Malczak


2016-10-10 14:35 GMT+02:00 Jay Abbott <jay at abbott.me.uk>:
> Is this what you're trying to achieve, only using a nicer syntax to
> represent it?
> http://swiftlang.ng.bluemix.net/#/repl/57fb8ac27365890cc848f831
>
>
> On Mon, 10 Oct 2016 at 13:04 Mateusz Malczak <mateusz at malczak.info> wrote:
>>
>> I think, I have used quite unfortunate naming, which is a root of an
>> misunderstanding here. By saying 'enums with stored properties' what I
>> was really thinking about, was enumeration type with stored constant,
>> immutable properties (constants). I don't want to duplicate 'struct'
>> type here, but instead I would like to make it possible to store a
>> const values in enumeration cases. So going back to my example once
>> again:
>>
>> Lest define an enumeration type `Format` with 3 possible cases. Each
>> case will be able to carry over some additional information - in this
>> case a pair of numbers (but in fact Any? should be possible)
>>
>> enum Format {
>>     case SMALL(30, 30)
>>     case MEDIUM(60, 60)
>>     case LARGE(120, 120)
>>     var width: Double
>>     var height: Double
>>     init(width: Double, height: Double) {
>>         self.width = width
>>         self.height = height
>>     }
>> }
>>
>> I'm not sure about 'var' clause in that example as it causes all the
>> confusion.
>>
>> I can access additional info stored in enum case, but it cannot be
>> modified. Format.SMALL doesn't change, as well as non of its
>> properties.
>>
>> // allowed usage
>> let format = Format.SMALL
>> let width = format.width // this would be equal to 30 (const value
>> assigned to 'width' property on enum case .SMALL)
>>
>> // not allowed usage
>> let format = Format.SMALL
>> format.width = 40 // error, stored values are immutable and can not be
>> modified
>>
>> We get all advantages of enumeration type, and, assuming all cases are
>> describing the same possible state, we can store some extra
>> information in each case. This can be called a third enumeration type
>> feature, right next to associated values and rawType.
>>
>> --
>> | Mateusz Malczak
>>
>>
>> 2016-10-10 13:40 GMT+02:00 Jay Abbott <jay at abbott.me.uk>:
>> > Thanks for the explanation Mateusz, I think I understand. So the enum
>> > still
>> > only has 3 cases, SMALL, MEDIUM, and LARGE, but an instance also has
>> > some
>> > properties?
>> >
>> > So some code to use it might be:
>> > var aFormat = Format.LARGE
>> > aFormat.width = 150 // aFormat is still Format.LARGE - this doesn't
>> > change
>> >
>> > Is that right?
>> >
>> > On Mon, 10 Oct 2016 at 09:06 Mateusz Malczak via swift-evolution
>> > <swift-evolution at swift.org> wrote:
>> >>
>> >> Hi,
>> >> > Perhaps it is a bit ugly, but I don’t know if allowing stored
>> >> > properties
>> >> > on
>> >> > enums is the solution: that looks very ugly to me too.
>> >>
>> >> That may look ugly, but can be very useful, if only you think
>> >> rawValue's are useful then you should also agree that stored
>> >> properties would be useful :)
>> >>
>> >> --
>> >> | Mateusz Malczak
>> >>
>> >>
>> >> 2016-10-10 9:26 GMT+02:00 David Hart via swift-evolution
>> >> <swift-evolution at swift.org>:
>> >> > Perhaps it is a bit ugly, but I don’t know if allowing stored
>> >> > properties
>> >> > on
>> >> > enums is the solution: that looks very ugly to me too.
>> >> >
>> >> > On 10 Oct 2016, at 02:36, Erica Sadun via swift-evolution
>> >> > <swift-evolution at swift.org> wrote:
>> >> >
>> >> > I would love to be able to have stored properties in addition to the
>> >> > varying
>> >> > elements.
>> >> >
>> >> > Now, I end up creating a secondary struct T and doing case a(T,
>> >> > whatever),
>> >> > b(T, whatever), c(T, whatever), etc. where the same associated
>> >> > structure
>> >> > is
>> >> > every case, *or* I end up putting the enum into a struct which means
>> >> > the
>> >> > guiding semantics are the struct and not the enumeration. Both
>> >> > approaches
>> >> > are ugly.
>> >> >
>> >> > -- E
>> >> >
>> >> > On Oct 9, 2016, at 6:03 PM, Jay Abbott via swift-evolution
>> >> > <swift-evolution at swift.org> wrote:
>> >> >
>> >> > Mateusz,
>> >> >
>> >> > To me, "Enumeration defines a type with well defined set of possible
>> >> > values"
>> >> > seems to contradict the idea of having properties that can have
>> >> > different
>> >> > values. What could you do with this special enum - what would the
>> >> > code
>> >> > that
>> >> > uses it look like?
>> >> >
>> >> >
>> >> >
>> >> > On Sun, 9 Oct 2016 at 04:56 Robert Widmann via swift-evolution
>> >> > <swift-evolution at swift.org> wrote:
>> >> >>
>> >> >> I’ve started doing this to try and mimic “Smart Constructors” in
>> >> >> Haskell
>> >> >> and I think it works quite well.
>> >> >>
>> >> >> struct Format {
>> >> >>   enum FormatBacking {
>> >> >>     case SMALL(Int, Int)
>> >> >>     case MEDIUM(Int, Int)
>> >> >>     case LARGE(Int, Int)
>> >> >>   }
>> >> >
>> >> >
>> >> > _______________________________________________
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>> >> > swift-evolution at swift.org
>> >> > https://lists.swift.org/mailman/listinfo/swift-evolution
>> >> >
>> >> >
>> >> >
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