Stack-allocated arrays

[KennyTM~]

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 :).