operator+ is now efficient (potentially more so than using a StringBuilder if you can do it all in one statement). operator+= still sucks, and I don't think we came up with an obvious way to get good performance with the same syntax. One possibility: we could add operator+=(String&) to StringBuilder rather than String. Then you could use the sugary operator syntax with the efficient class.
Regards, Maciej On Sep 4, 2012, at 4:27 PM, Dirk Schulze <dschu...@adobe.com> wrote: > I thought we had efforts to make String::operator+= use StringBuilder > somehow? I can remember that we had a discussion on webkit-dev and definitely > on bugzilla about improving String::operator+= instead of replacing it with > StringBuilder. > > Greetings, > Dirk > > On Sep 4, 2012, at 4:22 PM, Adam Barth <aba...@webkit.org> wrote: > >> As part of the work to deploy efficient string patterns [1] throughout >> WebKit, Benjamin and I noticed a bunch of very inefficient code that >> uses operator+= with Strings: >> >> String foo; >> for (...) >> foo += [...]; >> return foo; >> >> This pattern is particularly inefficient because += mallocs an >> entirely new buffer for the result and copies the the string into the >> new buffer. That means that this pattern makes O(n) calls to malloc >> and does O(n^2) work. A more efficient pattern is to use >> StringBuilder: >> >> StringBuilder foo; >> for (...) >> foo.append([...]); >> return foo.toString(); >> >> I'm in the process of going through WebCore and removing all callers >> of WTF::String::operator+=. Once that's complete, my plan is to >> remove WTF::String::operator+= from WTFString.h. Hopefully that will >> nudge contributors and reviewers towards more efficient string >> patterns. >> >> Removing operator+= will likely require changes to a number of >> port-specific files. I'll do my best to remove these, but I might >> need some help from maintainers of individual ports. If you're >> interested in helping out, please let me know. >> >> Many thanks, >> Adam >> >> [1] http://trac.webkit.org/wiki/EfficientStrings >> _______________________________________________ >> webkit-dev mailing list >> webkit-dev@lists.webkit.org >> http://lists.webkit.org/mailman/listinfo/webkit-dev > > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > http://lists.webkit.org/mailman/listinfo/webkit-dev _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
