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

[Robert Bennett]

It's not just about the cost of allocation; heap accesses are incredibly slow compared to stack accesses.

> On May 30, 2017, at 5:36 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> 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.
> 
> 
>> 10 000 may have been David's exageration, but imagine trying to form a chessboard using tuples - aside from the fact that you can't iterate over the tuple, the tuple type would be huge - instead of ChessPiece[8][8] (or similar syntax), you get:
>> 
>> ((ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece),
>> (ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece),
>> (ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece),
>> (ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece),
>> (ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece),
>> (ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece),
>> (ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece),
>> (ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece, ChessPiece))
>> 
>> And the practical use isn't just games - just think of any fixed-size matrices.
>> 
>>> On May 30, 2017, at 12:25 PM, Pavol Vaskovic via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>>> On Tue, May 30, 2017 at 7:51 AM, David Sweeris <davesweeris at mac.com> wrote:
>>>> 
>>>> `(Int, Int, Int, Int)` isn't *that* horrible compared to "[Int x 4]", but would you want to replace "[Int8 x 10000]" with the multipage-long tuple equivalent?
>>> 
>>> 😳
>>> It would be really helpful to my understanding, if you spoke about a practical use case. This reads as a contrived counterexample to me…
>>> 
>>> If your type really has 10 000 values in it, why does it have to be static, why doesn't normal Array fit the bill?
>>> 
>>> --Pavol
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