As with these end checks, what if dereference would throw exceptions? End checks gone, all the way up the stack...
Unfortunately not.
This simply moves the check into the dereference operation Also, remember that a filter_iterator dereferences iterator in it's operator++, so you the number of comparisons is unchanged.
class filter_range { reference increment_and_dereference() throw( at_end ) { // If reference is value_type&, this method has // no local variables with dtor, so it needs no exception frame. // Building one would negate any performance gain. for(;;) { reference t=base.increment_and_dereference(); if( pred(t) ) return t; } } void increment() { try { increment_and_dereference(); } catch( at_end& ) {} } reference dereference() const { return base.dereference(); } }; class base_range() { ... reference increment_and_dereference() throw( at_end ) { if( empty() ) throw at_end(); increment(); return dereference(); } }; I have not thought about whether other adaptor_ranges (difference, union, ...) could also use the increment_and_dereference idiom, so that mixed-type stacks (which are the really interesting ones) could be built. Arno -- Dr. Arno Schoedl · aschoedl@think-cell.com Technical Director think-cell Software GmbH · Invalidenstr. 34 · 10115 Berlin, Germany http://www.think-cell.com · phone +49-30-666473-10 · toll-free (US) +1-800-891-8091 Directors: Dr. Markus Hannebauer, Dr. Arno Schoedl · Amtsgericht Charlottenburg, HRB 85229