On Sunday, December 09, 2012 21:02:14 Mehrdad wrote: > So basically, algorithms should _expect_ copying of arbitrary > objects to be expensive, and there's no need for them to be > otherwise. C++'s swap() illustrates the lack of the need for > copying beautifully -- often times the only objects I copy > "generically" in C++ are iterators. I never find the need to copy > other objects... and I believe D has no such need, either.
It's been a debate for some time whether Phobos should be able to rely on copying being cheap. Algorithms end up copying all the time, and it greatly simplifies things if you don't have to worry about copying being expensive. Being able to rely on copying being O(1) is something that Andrei has tried to push for, but I don't see how we really can given simple things like the need to dup arrays - though I can see arguing that it's up to the caller to make copying cheap if they want certain algorithms to be more efficient. The whole reason that the move* primitives were introduced was to try and combat expensive copying, but they complicate things a fair bit and rarely get used, even if they should be. D's move semantics also help, but ultimately, some things are just plain going to be expensive to copy, and I don't see how you can get around that without disallowing certain idioms, which would then cause a different set of problems. - Jonathan M Davis
