Eric Niebler schrieb:
Stefan Strasser wrote:
Dave Harris schrieb:
For example, from looking at the implementation it seems that the macro caches the end() value in a variable called _foreach_end.
it is cached, but why? end is end and stays end, unless it is invalidated.
Performance. Even when writing loops by hand, it's a good idea to save the result of .end() in a local to avoid repeated function calls that are not necessary. It's called "hoisting". It's one of the side-benefits of using FOREACH and std:: algorithms.
I think it's not worth it here. besides that it isn't a performance overhead on most containers you don't expect that from a keyword. and it is not consistent: char str[]={'a','b',0,0}; foreach(char c,str){ str[2]='c'; std::cerr << c << std::endl; } output is "abc". std::string str="ab"; foreach(char c,str){ if(str.length() == 2) str+='c'; std::cerr << c << std::endl; } output is "ab". -- Stefan Strasser