Why is for() less efficient than foreach?

[biozic via Digitalmars-d-learn]

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];
}
```

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