Often repeated array allocations

[Namespace]

On Sunday, 21 July 2013 at 09:16:47 UTC, Jacob Carlborg wrote:
> On 2013-07-21 08:45, Namespace wrote:
>> But D isn't like Ada. It's more like C++ and there Heap 
>> allocations is
>> often used too.
>> It would be really cool if we had allocators already.
>> Something like:
>> ----
>> with (AllocatorX) { /// will use malloc and free instead of 
>> calling the GC
>>     float[] arr;
>>     arr ~= 42;
>> }
>> ----
>>
>> And I still don't know what a 'TLS scratch pad buffer' is.
>
> Perhaps:
>
> float[4000] scratchPadBuffer;
>
> void foo ()
> {
>     // use scratchPadBuffer here
> }
>
> I guess he just refers to a some temporary data you need during 
> the execution of a function and at the end of the function you 
> don't care about it.

But then I have mostly far too much and maybe a few times a bit 
too less store. It's not flexible. But maybe with a smaller 
granule.
What's about this:

----
struct Chunk(T, ushort maxSize = 1024) {
public:
	static T[maxSize] _chunk;

	T* ptr;
	size_t length;
	size_t capacity;

	this(size_t capacity) {
		this.capacity = capacity;

		if (capacity < maxSize)
			this.ptr = &_chunk[0];
		else
			this.ptr = cast(T*) .malloc(this.capacity * T.sizeof);
	}

	@disable
	this(this);

	~this() {
		if (this.ptr && this.capacity > maxSize)
			.free(this.ptr);
	}

	void ensureAddable(size_t capacity) {
		if (capacity > this.capacity) {
			this.capacity = capacity;

			if (this.capacity > maxSize)
				this.ptr = cast(T*) .realloc(this.ptr, this.capacity * 
T.sizeof);
		}
	}

	void opOpAssign(string op : "~", U)(auto ref U item) {
		this.ptr[this.length++] = cast(T) item;
	}

	void opOpAssign(string op : "~", U, size_t n)(auto ref U[n] 
items) {
		foreach (ref U item; items) {
			this.ptr[this.length++] = cast(T) item;
		}
	}
}
----