[swift-evolution] [Proposal] Enum subsets

[T.J. Usiyan]

Sub typing is the answer that we're going with then?

On Sat, Jun 4, 2016 at 4:26 PM, T.J. Usiyan <griotspeak at gmail.com> wrote:

> It could be a more general solution. I am unclear about what 'subtype
> relationships' means here though.
>
> Are you talking a about what you allude to here?
> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151130/000525.html
>
>
> The benefit of explicitly narrowing, in my opinion, is that there is no
> unnecessary cost to figuring out lookup. (Please correct me if I am
> mistaken.) Implicit promotions introduce uncertainty with regard to what a
> value is being treated as in any given moment. This uncertainty is worth it
> in many cases but I will suggest that it is not worth it when trying to
> deal with a narrower set of cases from an already established set. For
> example, in the graph/lattice situation, conversions must be written
> because there is no reasonable conversion that can be assumed. In this
> proposal, the conversion is obvious and trivial because the relationship is
> completely clear.
>
> All of that said, I *am* unclear about what subtype relationships means so
> it may very well be a better solution. It certainly sounds like a more
> general solution but I am not convinced that that is an advantage when
> trying to deal with a strict subset.
>
> TJ
> On Sat, Jun 4, 2016 at 1:25 AM, Chris Lattner <clattner at apple.com> wrote:
>
>>
>> On Jun 3, 2016, at 2:35 PM, T.J. Usiyan via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> Since this seems to have some interest, I've made a gist.
>>
>> https://gist.github.com/griotspeak/963bc87a0c244c120264b11fb022d78c
>>
>>
>> We have frequently discussed introducing subtype relationships between
>> structs and enums, in an effort to allow limited implicit promotions (e.g.
>> from small integers to wider integers).  Wouldn’t that be a more general
>> solution to this same problem?
>>
>> -Chris
>>
>>
>
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