[swift-evolution] Reduce with inout

Russ Bishop xenadu at gmail.com
Sat Jan 21 00:37:37 CST 2017

> On Jan 16, 2017, at 9:43 AM, Charles Srstka via swift-evolution <swift-evolution at swift.org> wrote:

> I don’t even know how long it actually takes to finish this test, because the last time I did this I eventually got sick of waiting and killed the process. So, I don’t know quite how many orders of magnitude slower it is, but it’s a lot.

That’s all the endorsement I need. +1 from me.

I do wonder if there is any way to get this sort of optimization out of the compiler. I suppose it would be difficult because the compiler doesn’t know what the mutable vs immutable pairs are or if such a pair even exists (array doesn’t have appending()).

If we assume + for Array had a mutating variant ala func + (lhs: inout Array, rhs: Array) { … }, would the compiler be able to prefer the inout version? What if a type wanted to offer a specialized version of a function for the compiler to call when the compiler can prove only temporaries are involved? I don’t want to go too far down the road of move constructors and whatnot for that way lies madness.

(Not a compiler expert, just wondering if there is a way to make situations like this into a “pit of success”).

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