[swift-evolution] Yet another fixed-size array spitball session

[Anders Kierulf]

> On May 30, 2017, at 3:36 PM, Jean-Daniel via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> 
>> Le 30 mai 2017 à 12:42, Charlie Monroe via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>> 
>> There was someone a few weeks ago trying to port his Go game to Swift from (I believe) C++ and found out that the lack of fixed-size arrays was causing the move-computing algorithm to slow down significantly.
>> 
>> This is due to fixed arrays being able to live on stack, while "normal Array" is dynamically allocated on heap, etc.
> 
> Really ? Isn’t it due to the value semantic of swift arrays ?
> 
> If this is the former, its algorithm can probably be tweak to reuse the array and require less allocations.
> 
> Unless if you algorithm is eager in memory allocation/deallocation, you shouldn't get a significant difference between static array and dynamic array.

Eliminating the dynamic allocations and extra indirections caused by the Swift array implementation can make a huge difference, not just in itself, but it also gives the compiler more opportunities to optimize the code. In my code (Monte Carlo simulations for a Go-playing program) I was able to gain a factor of 5 by using the ugly workaround of importing fixed-size arrays from C.

Anders

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