llvm dev - Dec 2016 - Openness to a "zip_iterator" type?

One of my coworkers noticed that we(Clang/LLVM) have quite a few places where we
need to iterate through 2 equally sized ranges at the same time, often related
to parm/arg relationships.  In a few cases we(Clang/LLVM) use a traditional
for-loop with 2 iterators in it.  In a few others, the implementation uses
range-for over 1 range with an iterator pattern on the other.

IMO, the correct solution to this would be a templated 'zip' type
(similar, though not identical to
http://www.boost.org/doc/libs/1_62_0/libs/iterator/doc/zip_iterator.html) that
would permit:

for (auto&& things : IteratorZip(ParmRange, ArgRange)) {
[CurParm, CurArg] = things; // things is a tuple that contains a reference to
each value
}


If I were to implement this IteratorZip type for the LLVM codebase, would this
be something the community would be interested in/accept/use?  Am I missing an
obvious existing implementation somewhere?

Thanks,
Erich

> On Dec 14, 2016, at 9:37 AM, Keane, Erich via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> One of my coworkers noticed that we(Clang/LLVM) have quite a few places
where we need to iterate through 2 equally sized ranges at the same time, often
related to parm/arg relationships.  In a few cases we(Clang/LLVM) use a
traditional for-loop with 2 iterators in it.  In a few others, the
implementation uses range-for over 1 range with an iterator pattern on the
other.
> 
> IMO, the correct solution to this would be a templated 'zip' type
(similar, though not identical to
http://www.boost.org/doc/libs/1_62_0/libs/iterator/doc/zip_iterator.html) that
would permit:
> 
> for (auto&& things : IteratorZip(ParmRange, ArgRange)) {
> [CurParm, CurArg] = things; // things is a tuple that contains a reference
to each value
> }
> 
> 
> If I were to implement this IteratorZip type for the LLVM codebase, would
this be something the community would be interested in/accept/use?  Am I missing
an obvious existing implementation somewhere?
Yes: include/llvm/ADT/STLExtras.h has zip.
See also unittests/ADT/IteratorTest.cpp.

— 
Mehdi

Inline post, sorry for the formatting, Outlook is terrible for editing mailing
lists

-----Original Message-----
From: mehdi.amini at apple.com [mailto:mehdi.amini at apple.com] 
Sent: Wednesday, December 14, 2016 9:41 AM
To: Keane, Erich <erich.keane at intel.com>
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Openness to a "zip_iterator" type?

> On Dec 14, 2016, at 9:37 AM, Keane, Erich via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> One of my coworkers noticed that we(Clang/LLVM) have quite a few places
where we need to iterate through 2 equally sized ranges at the same time, often
related to parm/arg relationships.  In a few cases we(Clang/LLVM) use a
traditional for-loop with 2 iterators in it.  In a few others, the
implementation uses range-for over 1 range with an iterator pattern on the
other.
> 
> IMO, the correct solution to this would be a templated 'zip' type
(similar, though not identical to
http://www.boost.org/doc/libs/1_62_0/libs/iterator/doc/zip_iterator.html) that
would permit:
> 
> for (auto&& things : IteratorZip(ParmRange, ArgRange)) { [CurParm, 
> CurArg] = things; // things is a tuple that contains a reference to 
> each value }
> 
> 
> If I were to implement this IteratorZip type for the LLVM codebase, would
this be something the community would be interested in/accept/use?  Am I missing
an obvious existing implementation somewhere?
Yes: include/llvm/ADT/STLExtras.h has zip.
See also unittests/ADT/IteratorTest.cpp.
[Keane, Erich] Awesome, thank you very much!  I am amazed my search didn't
turn this up, but I WAS amazed (apparently incorrectly!) that it was missing.
Thank you very much!

—
Mehdi