Pavol Droba wrote:
Hi,
First of all, I'd like to thank you for the nice benchmarks.
Now my comments to your patches:
1.) const Predicate& Pred Although this change can bring a performance benefits, it has one big drawback. You cannot pass an ordinary C function as predicate. At least not in VC++ 7.1
I consider this is to be very important functionality, therefor it is implemented the way it is.
VC++ is correct here: in order to bind to that signature, one would have to create a "reference to const-function" type, but const-qualified functions are illegal types. However, I believe there may be a DR that *would* make this legal: gcc tends to be at the forefront of implementing these even if they haven't made it into an official std yet.
2.) std::locale()
I'm not a big fan of global objects when they are not necessary. Correct locale implementation should give only a very small footprint when instantiating std::locale(), since is all should be reference based. As seen from your benchmarks, there is great difference between g++ and msvc. On the other hand, the difference on the vc++ is so large, that it is worth considering.
In theory passing a locale by value should be cheap, and it's distressing to see that it's not. Note that caching a global locale object and doing something like: foo(const std::locale& l = get_cached_locale_object()); is *not* an option: the global locale can be changed at any time by calling std::locale::global, which would make the locales returned by get_cached_locale_object() and std::locale() non-equivalent. Sorry for the bad news :-( John.