On Thu, Oct 7, 2010 at 9:22 PM, Peter Dimov <pdimov@pdimov.com> wrote:
Daniel Walker wrote:
void do_stuff(boost::function<int(int)> f) { // ... if(f) { // Remove the exception safety guarantee for this block. boost::unsafe_function<int(int)> g = f; for(int i = 0; i < INT_MAX; ++i) g(i); } // ... }
This example implies that unsafe_function is inherently more efficient, but this need not be so. An empty function may point to throw_bad_function_call instead of NULL.
I don't believe efficiency is a significant issue. I tried to measure the difference in performance between boost::function and unsafe_function in a tight loop, and with gcc -02, the difference is on the order of hundreds of picoseconds; i.e. in optimized code on contemporary PC hardware, unsafe_function is not significantly more efficient. But of course, results will vary according to your optimizer. The main advantage I see in unsafe_function is that it could be useful in environments where throw_bad_function_call and/or compiler optimizations are unavailable, such as in some embedded systems. Daniel Walker