on Fri Sep 05 2008, "Giovanni Piero Deretta" <gpderetta-AT-gmail.com> wrote:
You're completely right about that, and there are even additional reasons that you didn't mention, as I realized a couple days ago. I didn't want to bring it up, though, because it doesn't change the fundamental reality. Just replace strided_iterator by another layer of filter_iterator.
Hum, but as long as an iterator contains only a range, you can always encapsulate it with no space overhead. a filter_iterator<filter_iterator<T* > > has sizeof(T*2) (assuming a stateless predicate), which is optimal.
First of all, there's other kinds of data that's redundant across pairs of iterators in a range hey, like the predicate! But let's ignore that for a moment. The range compression formula is: sizeof(range<X>) == 2*sizeof(X) - sizeof(common_data<X>::type) so when X is filter_iterator<Y>: sizeof(X) is 2*sizeof(Y) common_data<X>::type == Y so: sizeof(range<X>) == 2*(2*sizeof(Y)) - sizeof(Y) == 3*sizeof(Y) so if sizeof(filter_iterator<Y>) == sizeof(range<Y>) sizeof(filter_iterator<Y>) == sizeof(range<Y>) == 2*sizeof(Y) - sizeof(common_data<Y>::type) and when Y is filter_iterator<Z>, X is filter_iterator<filter_iterator<Z> > sizeof(Y) is 2*sizeof(Z) common_data<Y>::type == Z so: sizeof(range<Y>) == 2*(2*sizeof(Z)) - sizeof(Z) == 3*sizeof(Z) sizeof(filter_iterator<Y>) == 3*sizeof(Z) sizeof(range<X>) == 3*sizeof(Y) == 3*2*sizeof(Z) == 6*sizeof(Z) What am I missing? -- Dave Abrahams BoostPro Computing http://www.boostpro.com