John Femiani wrote:
From: Eric Niebler
I won't deny that the abstraction penalty of BOOST_FOREACH is not zero, but have either of you actually measured the overhead? I have, and I found BOOST_FOREACH to be about 5% slower than the equivalent hand-coded loop when compiler optimizations are turned on. It's really very small, and that 5% buys you a lot of expressivity. YMMV.
Where does the 5% come from? Which part of BOOST_FOREACH (which is way to advanced for me to understand) is the part that causes the most trouble with compilers? Is it the extra if statement trick that seems to be used to initialize the variable?
There is a nested for loop that executes once per iteration, and it's only there so that the iteration variable can be a reference. Its presence incurs an extra test and set of a hidden bool at each iteration. And on some compilers, there are a couple of extra Boolean checks before entering the loop. (Aside: please try to limit the amount of text you quote in your messages.) -- Eric Niebler Boost Consulting www.boost-consulting.com