Stack-allocated arrays

[Dave]

"Andrei Alexandrescu" <SeeWebsiteForEmail at erdani.org> wrote in message 
news:gff7g0$t54$1 at digitalmars.com...
> KennyTM~ wrote:
>> 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.
>
> This entire discussion gets me thinking - could an alternate stack be a 
> good (or even better) solution? Consider a global per-thread 
> "superstack" - a growable region that allocates memory in large chunks and 
> makes sub-chunks accessible in a strictly LIFO manner. The primitives of 
> the superstack are as follows:
>
> void* SuperStack.allocate(size_t bytes);
> void SuperStack.free(size_t bytes);
> size_t SuperStack.slack();
>
> The SuperStack's management is a singly-linked list of large blocks. The 
> slack function returns how many bytes are left over in the current chunk. 
> If you request more than slack bytes, a new chunk is allocated etc. A 
> SuperStack can grow indefinitely (and is susceptible to leaks).
>
> Some convenience functions complete the picture:
>
> T[] SuperStack.array(T)(size_t objects);
> enum Uninitialized { yeahIKnow }
> T[] SuperStack.array(T)(size_t objects, Uninitialized);
>
> Freeing chunks should not be done immediately in order to avoid 
> pathological behavior when a function repeatedly allocates and frees a 
> chunk just to fulfill some small data needs.
>
> With the SuperStack in place, code could look like this:
>
> void foo(in size_t s)
> {
>     auto a = SuperStack.array(int)(s, Uninitialized.yeahIKnow);
>     scope(exit) SuperStack.free(s);
>     ... play with a ...
> }
>
> Is there interest for such a thing?
>

That would be interesting and even better if it could be a built-in (not
clear on if that was the intention or not).

The reason for having it be a built-in is (IMO) it's important for D to
provide language constructs that can improve performance for common things
like allocating temporary, scope-limited arrays and classes, especially with
the new direction D2 discussions have been heading in lately (like pure
functions and such).

>
> Andrei