On Tuesday, 13 August 2019 at 22:12:23 UTC, Mirjam Akkersdijk
wrote:
Though, it left me with some semi-offtopic questions unanswered:
(1) Ali, do you mean that from an optimization viewpoint, it's
better to keep appending like `nodes ~= ...` instead of setting
the length first? I would like to have some more background on
that claim.
He's not saying it will be better, but that the cost will be
negligible. On every append, the GC allocates new memory only if
the current capacity == 0. When it does allocate, it allocates
more space than it actually needs based on the current length of
the array, so you don't actually have an allocation on every
append. Also, when the adjacent memory block is free and can hold
the additional elements, the allocation consists of extending the
array's memory block and no copying is performed, making the cost
of the allocation even cheaper than it could be.
Anyway, you can use `reserve` when appending rather than setting
the length. This will allocate enough memory without
default-initializing anything and you don't have to worry about
bounds checking.
int[] ints;
ints.reserve(100);
foreach(i; 0..100) {
ints ~= i;
}
See Steve Schveighoffer's array article for details:
https://dlang.org/articles/d-array-article.html
