foreach/iota countdown

[Ivan Kazmenko]

>> /home/alaran/tmp/test.d(5:16)[warn]: 3 is larger than 2. This 
>> slice is likely incorrect.
>> /home/alaran/tmp/test.d(6:22)[warn]: 20 is larger than 10. Did 
>> you mean to use 'foreach_reverse( ... ; 10 .. 20)'?
>
> Isn't foreach_reverse being deprecated?

Oh.  If so, what would be the right way to iterate backwards?  
The usual "for (*;*;*)" is too repetitive and error-prone: 
nothing is going to catch some "for (int i = 19; i >= 10; j--)" 
errors or the like.  Using ranges, such as iota and retro, 
currently results in a *massive* slowdown for DMD.

As a crude proof for the last statement, below are my local 
timings for DMD 2.064.2 on Win32 using "dmd -O -release -inline 
-noboundscheck" to compile.

Example 1 (0.38 sec):
void main () {foreach (i; 0..1_000_000_000) {}}

Example 2 (0.39 sec):
void main () {for (int i = 0; i < 1_000_000_000; i++) {}}

Example 3 (2.03 sec):
import std.range;
void main () {foreach (i; iota (1_000_000_000)) {}}

Unless simple things like example 3 run on par with the first 
two, foreach on ranges - or, in that regard, UFCS 
functional-style range chains without even a foreach - are just 
plain unacceptable in bottlenecks.  LDC is able to handle simple 
cases like this, but introducing a compiler dependency just 
because of this?  That would also be unfortunate.

Ivan Kazmenko.