Steven Schveighoffer wrote:
On Thu, 04 Mar 2010 11:43:27 -0500, grauzone <[email protected]> wrote:
Some sort of "resetAndReuse" function to clear an array, but enabling
to reuse the old memory would be nice:
int[] a = data;
a = null;
a ~= 1; //reallocates (of course)
a.length = 0;
a ~= 1; //will reallocate (for safety), used not to reallocate
resetAndReuse(a);
assert(a.length == 0);
a ~= 1; //doesn't reallocate
This can be implemented by setting both the slice and the internal
runtime length fields to 0.
Additionally, another function is necessary to replace the old
preallocation trick:
//preallocate 1000 elements, but don't change actual slice length
auto len = a.length;
a.length = len + 1000;
a.length = len;
As I understood it, this won't work anymore after the change. This can
be implemented by enlarging the array's memory block without touching
any length fields.
I'm sure the function you had in mind does one of those things or both.
proposed usage (as checked in a couple days ago):
int[] a;
a.setCapacity(10000); // pre-allocate at least 10000 elements.
foreach(i; 0..10000)
a ~= i; // no reallocation
a.length = 100;
a.shrinkToFit(); // resize "allocated" length to 100 elements
a ~= 5; // no reallocation.
What shrinkToFit() does is not really clear. Does it reallocate the
memory block of the array such, that no space is wasted? Or does it
provide (almost) the same functionality as my resetAndReuse(), and make
the superfluous trailing memory available for appending without
reallocation?
I think a resetAndReuse is really needed. I have found it can prevent
"GC thrashing" in many cases. E.g. when caching frequently re-evaluated
data in form of arrays (free previous array, then allocate array that
isn't larger than the previous array).
