Re: Why does array loses it internal capacity on length change?

[Adam D. Ruppe via Digitalmars-d-learn]

On Saturday, 12 March 2016 at 09:56:48 UTC, Uldis wrote:

Why is this happening, how to avoid it?


Details here: http://dlang.org/d-array-article.html

it is so one slice can never stomp over the contents of another 
slice when you append to it.


array.assumeSafeAppend() can override it.

Re: Why does array loses it internal capacity on length change?

[Jack Applegame via Digitalmars-d-learn]

Why is this happening...?
For safety reasons. Your array can be shared between parts of 
application.

...how to avoid it?

https://dlang.org/library/object/assume_safe_append.html

Why does array loses it internal capacity on length change?

[Uldis via Digitalmars-d-learn]

While writing a structs function that I wanted to minimize 
allocations and use an internal preallocated buffer, but I 
noticed that arrays are losing their capacity when its length is 
changed.


For example:

void main() {

int[] a;
a.reserve = 1024;

void dump(in ref int[] b,size_t line = __LINE__) {
import std.stdio;
writeln(line, ": Buffer length = ", b.length, " 
capacity= ", b.capacity);

}
dump(a); // line 10
a.length = 0;
dump(a);
a ~= [1,2,3];
dump(a);
a.length = 0;
dump(a);
a ~= [4,5,6];
dump(a);
}

gives output:

10: Buffer length = 0 capacity= 2043
12: Buffer length = 0 capacity= 2043
14: Buffer length = 3 capacity= 2043
16: Buffer length = 0 capacity= 0
18: Buffer length = 3 capacity= 3

but I expected:

10: Buffer length = 0 capacity= 2043
12: Buffer length = 0 capacity= 2043
14: Buffer length = 3 capacity= 2043
16: Buffer length = 0 capacity= 2043
18: Buffer length = 3 capacity= 2043


Why is this happening, how to avoid it?