C++11

C++1x loses Concepts

Posted on July 22, 2009

Bjarne Strous­trup and Herb Sut­ter have both re­ported on the ISO C++ meet­ing in Frank­furt a week ago, in which the much-her­alded fea­ture "con­cepts" were re­moved from C++1x.

Con­cepts are a pow­er­ful fea­ture aimed at im­prov­ing over­load­ing (ba­si­cally, re­mov­ing the extra work in using things like it­er­a­tor cat­e­gories) and mov­ing type check­ing up the lad­der so that more rea­son­able error mes­sages can be pro­duced when a de­vel­oper passes in the wrong type (think a sin­gle error line in­stead of mul­ti­ple pages of tem­plate crap). Ap­par­ently the fea­ture was a lot less solid than most of us thought, with a huge amount of in­ter­nal ar­gu­ing within the com­mit­tee on a lot of the fun­da­men­tal fea­tures of it. It seems that while most agreed con­cepts were a good idea, no­body could agree on how to im­ple­ment them.

I'm def­i­nitely dis­ap­pointed by this, but I'm also glad they chose to re­move con­cepts in­stead of fur­ther de­lay­ing the stan­dard, or worse putting out a poorly de­signed one. In­stead, it seems like there is hope for a smaller C++ up­date to come out in 4-5 years that adds a more well thought out con­cepts fea­ture. There are plenty of other C++1x lan­guage fea­tures to be happy about for though, like vari­adic tem­plates, rvalue ref­er­ences, and lambda func­tions!

You may no­tice I've been say­ing C++1x here in­stead of C++0x—that's be­cause it's pretty ob­vi­ous to every­one now that we won't be get­ting the next C++ stan­dard in 2009, but more likely 2011 or 2012. Just in time for the end of the world!