Hi, On Thu, Jul 19, 2012 at 02:03:39PM -0700, julien2412 wrote: > Thank you David for the hint! > I re read the "An in-depth explanation" part of > http://stackoverflow.com/questions/3279543/what-is-the-copy-and-swap-idiom/3279550#3279550, > it's great ! I understood when and above all how the memory is cleaned. > > About your multidimalgorithm, what would be the problem if it'd be changed > like this ? (to sum up: passing parameter by value to optimize) > > /include/mdds/flat_segment_tree.hpp > > flat_segment_tree<key_type, value_type>& > operator=(flat_segment_tree<key_type, value_type> other); > > /include/mdds/flat_segment_tree_def.inl > template<typename _Key, typename _Value> > flat_segment_tree<_Key, _Value>& > flat_segment_tree<_Key, _Value>::operator=(flat_segment_tree<_Key, > _Value> > other) > { > swap(copy); > return *this; > }
It is equivalent to the current code. Just most C++ programmers (including me :-) are accustomed to the "fact" that operator= takes its argument by const reference... > > this part of > http://stackoverflow.com/questions/3279543/what-is-the-copy-and-swap-idiom/3279550#3279550 > made me think about this: > Observe that upon entering the function that all the new data is already > allocated, copied, and ready to be used. This is what gives us a strong > exception guarantee for free: we won't even enter the function if > construction of the copy fails, and it's therefore not possible to alter the > state of *this. (What we did manually before for a strong exception > guarantee, the compiler is doing for us now; how kind.) Yeah, it is even a line shorter :-) But whether a function call is (not) eliminated in the case an exception is thrown would be the last of my worries (it is _exceptional_ situation, after all... And the gain of avoiding the call would be more than offset by the cost of the exception processing mechanism.) > > Is this design pattern without flaw (does it exist ? :-)) and be applied in > every case in LO code ? Well, we do not typically care so much about exceptions in LO (heck, there is code--and probably a lot of it--that does not even have weak exception guarantee). So it is probably not so useful to start adapting the assignment operators in our codebase en masse. D. _______________________________________________ LibreOffice mailing list LibreOffice@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/libreoffice
