|
Boost : |
From: Walker, Daniel (Daniel.Walker_at_[hidden])
Date: 2003-11-25 16:14:22
Hello,
I'm new to the list, but I was just thing about the utilities next() and
prior(), and I have a suggestion. I think it would be very useful to
have a next_n() and prior_n() to simulate operators + and - for non
random access iterators. Often, I find myself in the situation where I
know the length of a sequence, but don't have the last iterator. For
example, I'd like to process all subsequences of length three. This is
fairly simple with random access iterators ...
for(RandomAccessIterator i = first; i != last - 2; ++i)
{
RandomAccessIterator my_first = i, my_last = i + 3;
// ... do something
}
But with bidirectional iterators ...
BidirectionalIterator tmp_last = last;
std::advance(tmp_last, -2);
for(BidirectionalIterator i = first; i != tmp_last; ++i)
{
BidirectionalIterator my_first = i, my_last = i;
std::advance(my_last, 3);
// ... do something
}
What I'd like to be able to say is something like ...
for(BidirectionalIterator i = first; i != boost::prior_n(last, 2);
++i)
{
BidirectionalIterator my_first = i, my_last = boost::next_n(i,
3);
// ... do something
}
The implementation would be straightforward.
template <class T, class Size>
inline T next_n(T x, Size n)
{
std::advance(x, n);
return x;
}
template <class T, class Size>
inline T prior_n(T x, Size n)
{
std::advance(x, -n);
return x;
}
Is there another way that I'm not aware of that would give me a similar
effect? If not, is there any interest in next_n() and prior_n()?
Thanks!
_________________________________
Daniel Walker, Software Engineer
Bowne Global Solutions
Office 5095 Murphy Canyon Road
San Diego, CA 92101 USA
Phone +1 858 737 5247
Mobile +1 619 251 4068
Fax +1 858 737 5297
daniel.walker_at_[hidden]
www.bowneglobal.com
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk