type variables

Schrom, Brian T Brian.Schrom at pnnl.gov
Sun Aug 2 15:51:40 UTC 2020

On Sun, Aug 02, 2020 at 03:04:07PM +0000, Paul Backus via Digitalmars-d wrote:
> In fact, the naive recursive version of iota is actually even simpler:
> int[] iota(int start, int finish)
> {
>     if (start > finish)
>         return [];
>     else
>         return [start] ~ iota(start + 1, finish);
> }
> Again, the problem with this function is not complexity or readability, but
> performance. It performs many unnecessary memory allocations, and consumes
> (finish - start) stack frames instead of 1.

I'm  disappointed that  the  code  as written  above  appears to  indeed
generate N stack frames from my looking with compiler explorer.

However, basically the  same version, to me, seems to  TCO, thus 1 stack
frame, with optimization turned on with ldc.

void iotaTCO( ref int[] array, int start, int finish)
    if (start > finish)
        array ~= start;
        iotaTCO(array, start + 1, finish);

I think I'm  missing the essence of what is  different between these two
functions and why TCO isn't applicable to the first.

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