[swift-evolution] [Proposal] Add support for compile-time function execution

L Mihalkovic laurent.mihalkovic at gmail.com
Sun Jun 12 03:47:52 CDT 2016

> On Jun 12, 2016, at 6:05 AM, Alexander Momchilov <alexandermomchilov at gmail.com> wrote:
> Aren't macros totally different?
> Anyways, weren't macros rejected? I thought Swift was trying to avoid having the hefty reliance of preprocessor macros that C did.

Sorry I was not referring to C-style macros (i.e. preproc). I was referring to a macro language in the sense of the scala compiler macros or other languages that let you insert compile time code inside your source (like D). I was of the opinion that it would be a short step to support something like embedded SIL inside string literals. But Chirs ruled out compile time code execution stressing that it should not be a replacement for designing a great language. Maybe around 4 or 5, when the language is mature, then compile time code execution (macros) can be added

>> On Jun 9, 2016, at 1:48 AM, L. Mihalkovic <laurent.mihalkovic at gmail.com <mailto:laurent.mihalkovic at gmail.com>> wrote:
>> Chris has rules macros out-of-scope for 3.0. Who knows, maybe they'll be allowable in 4.0
>> On Jun 9, 2016, at 1:41 AM, Alexander Momchilov via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> Preface: I know this is likely a large undertaking to implement, but I think it's worth it.
>>> In addition to the typical compiler optimization of constant math expressions, some languages (such as D and C++) have support for running arbitrary functions at compile time <https://en.wikipedia.org/wiki/Compile_time_function_execution> (with some constraints).
>>> I see many advantages of this:
>>> On iOS/OS X: it could precompute the UI and app initialization logic (wherever possible) to speed app load times
>>> It can significantly speed up the initialization of applications with large static properties. E.g. large constant Dictionaries could be precomputed.
>>> You could keep complex math expressions (including custom functions) in their unevaluated form, without the pressure to precompute them elsewhere and hardcode in the result.
>>> Dynamic programming: expensive look-up tables could be precomputed. These wouldn't necessarily be large in size, but if their elements are especially expensive to compute, there would be a huge advantage to precomputing them.
>>> What do you guys think? Can you think of any other useful applications? Would it be worth the implementation effort?
>>> - Regards,
>>>         Alexander Momchilov
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