Subject: Re: [boost] Boost range - Add variadic join/zip
From: Jeff Flinn (Jeffrey.Flinn_at_[hidden])
Date: 2013-05-10 10:31:10
On 5/10/2013 8:44 AM, Jonathan Wakely wrote:
> On 10 May 2013 12:55, Neil Groves wrote:
>> On Fri, May 10, 2013 at 11:28 AM, Jonathan Wakely
>>>
>>> It looks as though it's undefined behaviour to zip ranges of different
>>> lengths, because you'll walk off the end of the shorter ranges.
>>>
>> My variadic zip stops at the end of the shortest range, which seems to
>>> be consistent with zip functions in most other languages I've looked
>>> at.
>>>
>>>
>> I like being able to avoid the cost of checking for the end of every item
>> in the zip especially for non-random access iterators. In anything I put
>> into Boost.Range I think it of paramount importance to obey the zero
>> overhead principle. It seems that it would be simple to allow both end
>> detection mechanisms.
The closest existing practice I see is the std::mismatch algorithm which
requires the first of the two input sequences to be the longest, and
only checks first1 != last1.
boost::range::mismatch pays the overhead of checking both input sequence
iterators against their corresponding end iterators.
Perhaps the std::mismatch approach is appropriate for zip iterator as
well. In accommodating std::mismatch requirements when I don't know that
the first sequence is longest I've a wrapped mismatch that check's the
sizes and swaps argument references, though this is limited in it's
genericity.
Jeff