Why is for() less efficient than foreach?

[Bastiaan Veelo via Digitalmars-d-learn]

On Friday, 10 February 2017 at 12:57:38 UTC, biozic wrote:
> On Friday, 10 February 2017 at 12:39:50 UTC, Bastiaan Veelo 
> wrote:
>>     void foreach_loop()
>>     {
>>         foreach(n, elem; d[])
>>             elem = a[n] * b[n] / c[n];
>>     }
>
> It's fast because the result of the operation (elem) is 
> discarded on each iteration, so it is probably optimized away.
> Try:
> ```
> void foreach_loop()
> {
>     foreach(n, ref elem; d[])
>         elem = a[n] * b[n] / c[n];
> }
> ```

Hah, of course.

> You can also do:
> ```
> d = a[] * b[] / c[];
> ```
> with no loop statement at all.

Nice.

Thanks.