Fast temporary dynamic arrays? (And slicing of them)

[bearophile]

Tom Kazimiers:
> But good to know that it would work with backward growing of the
> array - do have you an example of that?

Just created:


import std.stdio: writeln;
import std.c.stdlib: alloca;

void main() {
    int n = 30;
    alias int T;
    enum int initialCapacity = 4;
    static assert(initialCapacity > 0);

    int len = 0;
    int capacity = initialCapacity;
    int* ptr = cast(int*)alloca(capacity * T.sizeof);
    ptr += initialCapacity - 1; // correct?

    foreach_reverse (i; 0 .. n) {
        if (i >= capacity) {
            alloca(capacity * T.sizeof);
            capacity *= 2;
        }
        ptr--;
        *ptr = i;
        len++;
    }

    writeln("len, capacity: ", len, " ", capacity);
    auto arr = ptr[0 .. len];
    writeln(arr);
}


Beware of stack overflows.

Bye,
bearophile