How do you deal with scoped allocations?

[Namespace]

On Sunday, 8 December 2013 at 09:14:44 UTC, Dmitry Olshansky 
wrote:
> 08-Dec-2013 02:32, Namespace пишет:
>> Since my last thread doesn't get much attention I like to ask 
>> here: How
>> did you deal with temporary memory? Let's assume that the size 
>> is only
>> known at runtime.
>> I have this situation e.g. in Dgame in the capture method: I 
>> get the
>> pixel data from my Window with glReadPixel but it is reversed. 
>> So I have
>> to reverse it again, but I still need at least temporary 
>> memory for one
>> pixel-line which stores the currently swapped pixels. So how 
>> would you
>> solve such a situation?
>>
>> Since D doesn't offer VLA's and alloca is broken (besides the 
>> ugly syntax),
>> I use a scoped wrapper (since scope doesn't do the job):
>>
>> ----
>> struct scoped(A : T[], T) {
>>     T[] arr;
>>
>>     alias arr this;
>>
>>     this(T[] arr) {
>>         this.arr = arr;
>>
>>         writefln("Get %d %s's (ptr = %x)", arr.length, 
>> T.stringof,
>> arr.ptr);
>>     }
>>
>>     ~this() {
>>         GC.free(this.arr.ptr);
>>         this.arr = null;
>>         GC.minimize();
>
> This is slow. Just use malloc & free, why touch GC at all?
>>     }
>> }
>>
>> void main() {
>>     // need temp memory
>>     scoped!(int[]) arr = new int[n];
>> }
>> ----
>>
>> And what do you use?

Because it's more D'ish. That is what D offers.
Why is it slower than malloc + free?