[phobos] phobos commit, revision 1871

[Jonathan M Davis]

On Sunday 15 August 2010 14:31:28 David Simcha wrote:
> I've added Lockstep to std.range, which allows things like:
> 
> foreach(a, b; lockstep(range1, range2)) {
>      // Loop body.
> }
> 
> If anyone really doesn't like it, it can be removed, but I've **really**
> wanted this functionality for a **long** time.
> 
> I considered integrating it into Zip, but decided against this because:
> 
> 1.  DMD doesn't currently work properly in terms of overloading
> opApply-based foreach against range-based foreach, even when there is no
> ambiguity.
> 
> 2.  Even if this gets fixed, there will still be ugly ambiguous cases if
> iterating with Proxy and iterating as individual variables are put in
> the same struct once bug 3444
> (http://d.puremagic.com/issues/show_bug.cgi?id=3444) gets fixed.
> 
> Using Zip for iterating in lockstep over ranges via foreach is just
> syntactically ugly enough that I never do it in practice.  This is
> mostly because I can't name the element variables individually and have
> to access them as members of a Proxy.  Zip has its place for things like
> sorting in lockstep, and I plan to improve/debug it, too, but I really
> felt that for simple foreach-based lockstep iteration, a separate struct
> was necessary.

The situation where you have to iterate over two separate ranges at the same 
time has always been a flaw in foreach that has irritated me (in any language 
that I've used). I haven't found it to be that big a deal, since you just turn 
it into a for loop, make it a bit more verbose, and you're fine, but being able 
to iterate over two ranges simultaneously with foreach would be a good thing. 
This looks like a good addition to Phobos.

- Jonathan M Davis