[swift-evolution] [Planning][Request] "constexpr" for Swift 5

[Daryle Walker]

> On Jul 30, 2017, at 5:34 PM, Tino Heth <2th at gmx.de> wrote:
> 
>> If you read my reply to Daniel Vollmer, you’ll find that we’re thinking about the exact same thing. 
> Good to hear — read that post later, but I guess repeating doesn't hurt here: People still talk about macros... ;-)
> 
>>> So while I think they’re both great features to have, I assume the core team will have higher priorities on their schedule, as I don’t see how these features wouldn’t eat up most resources for at least (!) one Swift release-cycle.
>> 
>> That’s just it: the core team is already prioritizing a lot of features that would greatly benefit from this. In fact, if this would be implemented, a large portion of the swift compiler could be moved into the standard library, because it wouldn’t be magic any more. This would single-handedly reduce the implementation time and effort of most proposals by a very large margin.
> 
> … and I like specific examples ;-), so out of my head, four features that people want to have and that could be added easily with "Meta-Swift":
> - Forwarding of protocol conformance (Kotlin, for example, has this: When a member conforms to a protocol, you don't have to write a bunch of methods that just say "let my member do this")
> - init with reduced boilerplate
> - Subtyping for non-class types, including a "newtype" option
> - Property behaviours

The first and third items in that list seem similar to the “strong type-alias” idea I just updated (at <https://gist.github.com/CTMacUser/c493f775075e946efdcfd85d38473291>). Is it close to what you’re talking about? I did the update because I recently looked up product and sum types again, and saw things called subtypes and quotient types. I realized that, with a little tweaking, strong-type-aliases could what would be needed to model sub- and quotient types.

> Imho the reflection capabilities that are needed to make the feature fly are the big tasks — using this information shouldn't be that hard, as it's just a explicit way of telling the compiler what to do.
> Assuming that reflection will be improved anyways, it might be a very cheap feature with huge benefit.

— 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com 

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