How do you remove/insert elements in a dynamic array without allocating?

[bearophile]

Malte Skarupke:

> void main()
> {
>     import core.memory;
>     GC.disable();
>     scope(exit) GC.enable();
>
>     int[] a = [1, 2, 3, 4, 5];
>     foreach(i; 0 .. 1000000000)
>     {
>         --a.length;
>         a ~= i;
>     }
> }
>
> That loop will keep on allocating in every iteration until your 
> memory is full.
>
> Is there a way to do something similar to this without 
> allocating?

void main() {
     auto array = [1, 2, 3, 4, 5];
     array.assumeSafeAppend();
     foreach (i; 0 .. 10_000_000) {
         array.length--;
         array ~= i;
     }
}



> But neither one works.

And that's good, it was designed that way on purpose :-)


> How do you work with the dynamic array without having to rely 
> on the GC all the time?

There are various ways to do it...


> I want something similar to the stl vector, which only 
> re-allocates once your array grows past a certain size, not on 
> every append.

D arrays already work like this.

Bye,
bearophile