Den 01-02-2012 18:02, Mathias Gaunard skrev:
On 02/01/2012 04:39 PM, Beman Dawes wrote:
A question came up in a long bikeshed discussion on a C++ committee mailing list as to the performance of range based interface versus a begin/end iterator interface (I.E. traditional STL interface) to the same algorithms.
It's exactly the same performance, because a range is just a pair of begin/end iterators and all the code is implemented using the iterators.
Well, sometimes the high-leve range adaptors can make better decisions. For exmple, assuming the adaptors don't turn the iterators into bidirectional iterators, boost::push_back( out_range, ... ) will only grow the output vector once. Of course, the old version can call reserve(), if people remember that. OTOH, range adaptors sometimes inhibit (manual) loop-unrolling. For example, copy_if( ... ) can unroll the inner loop for random access iterator wheres copy( ... | filtered(...) ...) cannot. I suspect that the difference is minor because the iterator comparison will be dwarfed by the cost of calling the predicate and copying the value. -Thorsten