Hi Chris, On Mon, 16 Sep 2002, Chris Russell wrote: cdr> p.156 of the BGL book: "... visitors are passed by value..." cdr> cdr> I was attempting to set a breakpoint in a visitor event handler (that cdr> I know is executing) but the breakpoint is seemingly ignored by my cdr> debugger. This is because the visitor I construct and subsequently cdr> pass to the algorithm is not the object that is actually dispatched cdr> by the algorithm. Correct? Using the Intel compiler under MS Yes, that is correct. cdr> DevStudio 6 on Windows, I inserted a ::DebugBreak() (asm int 3) into cdr> the visitor and *do* hit that but only have assembly language and not cdr> source to step through at that point. cdr> cdr> Why are visitors passed to algorithms by value? Any suggestions for Well, visitors are like functors, and the STL passes functors by-value. There are some non-trivial reasons for that decision that I don't have time to go into now. cdr> debugging visitor code at the C++ source level and not in assembly? cdr> Sorry, I don't have a lot of experience with that debugger. Regards, Jeremy ---------------------------------------------------------------------- Jeremy Siek http://php.indiana.edu/~jsiek/ Ph.D. Student, Indiana Univ. B'ton email: jsiek@osl.iu.edu C++ Booster (http://www.boost.org) office phone: (812) 855-3608 ----------------------------------------------------------------------