Stack-allocated arrays

[Janderson]

KennyTM~ wrote:
> Janderson wrote:
>> KennyTM~ wrote:
>>> Janderson wrote:
>>>> Dave wrote:
>>>>>> I'd love for "scope foo = new T[len];" to do for arrays what 
>>>>>> "scope bar = new Class;" does for classes. And indeed, if it's too 
>>>>>> big the compiler
>>>>>
>>>>> I'm surprised it doesn't and see that as a bit inconsistent, with 
>>>>> the only serious argument against it being that 'scope' couldn't be 
>>>>> used for large dynamic arrays.
>>>>>
>>>>> But then again:
>>>>>
>>>>> class C
>>>>> {
>>>>>   int[264_000] a;
>>>>> }
>>>>>
>>>>> void foo()
>>>>> {
>>>>>    scope C c = new C;
>>>>>    ...
>>>>> }
>>>>>
>>>>> could also overflow the stack. In either case the work-around would 
>>>>> be the same (increase the stack size or not use 'scope').
>>>>>
>>>>
>>>> As a work around, I imagine it would be possible to write a template 
>>>> that used the above syntax with a static if that would change 
>>>> depending on the size:  Something like this (untested):
>>>>
>>>>
>>>> class FastArray(T, int size)
>>>>     if (size < 1000)
>>>> {
>>>>     T[size] a;
>>>>     ... Overload operators
>>>> }
>>>>
>>>> class FastArray(T, int size)
>>>>     if (size >= 1000)
>>>> {
>>>>     T a[] = new T[size];
>>>>     ... Overload operators
>>>> }
>>>>
>>>>
>>>> //Use
>>>>
>>>> void foo()
>>>> {
>>>>     scope FastArray array = new FastArray!(int, 10); //Stack
>>>>     scope FastArray array = new FastArray!(int, 10000); //Heap
>>>> }
>>>>
>>>> Of course you never know where you are in the stack, so nesting 
>>>> these to much would be bad.
>>>
>>> But this won't work if size is runtime-determined.
>>
>> Thanks for clarifying my last point :)
>>
>> -Joel
> 
> Is it? I mean things like:
> 
>   int size = read_from_stdin();
>   scope array = new FixedSizeArray!(int)(size);
> 
> You can't do it FixedSizeArray!(int, size) because all template 
> arguments must be determined at compile time.
> 
> The best solution I can think of, without compiler modification is a 
> struct/class that contains a static array member T[1024] and a dynamic 
> array member T[] initialized to null; and the code chooses which member 
> to use in the constructor. But this always occupies 1024*T.sizeof bytes 
> and there will always be a conditional (if) sticked to all access methods.
> 
> I hope I don't misunderstand your last point :).

I assumed you knew the size at compile time (like in Dave's example) and 
wanted to avoid stack overflow.  Modifying the stack at compile time 
would be a dangerous thing.  I think the best solution would be to have 
a second stack for that sort of thing, which could be managed in a 
library still.

-Joel