On Tue, Mar 3, 2009 at 2:15 PM, Steven Watanabe <watanabesj@gmail.com> wrote:
Emil Dotchevski wrote:
On Tue, Mar 3, 2009 at 1:26 PM, Steven Watanabe <watanabesj@gmail.com> wrote:
Emil Dotchevski wrote:
2) convert<std::string> necessarily returns std::string (I think it's important user-defined conversions to have the freedom to return char const *. Many interfaces that take strings are commonly overloaded for std::string and char const * for efficiency reasons.)
How common is this going to be in reality? Won't returning const char* usually introduce problems with memory management?
I think that whether this is common or not is not important, my point is that it is a valuable optimization technique.
I don't think it is. It's too fragile. Functions taking const char* arguments don't have the same problems.
Functions that take char const * arguments are the reason why it's important to allow for to-string conversions to return char const *.
If conversion of objects of type foo to string is for some reason critical for performance, you can have foo contain a std::string and make its to-string overload return a char const *, through std::string::c_str().
which will work fine, until some generic code converts a temporary to a string.
What you probably mean is that if to_string returns char const *, the following would be undefined: char const * to_string( foo const & ); foo bar(); char const * s=to_string(bar()); //oops That's true, however this other scenario, where the foo object is also temporary, is valid: char const * to_string( foo const & ); foo bar(); void print( char const * ); void print( std::string const & ); print(to_string(bar())); So yes, it's tricky but it is still a valid optimization technique, IMO. We can specify to_string accordingly, saying that the returned object is only valid for the lifetime of the object being converted to string so the caller would know to do std::string s=to_string(bar()) which would be fine always. By the way, returning std::string doesn't guard against such errors: std::string to_string( foo const & ); foo bar(); char const * s=to_string(bar()).c_str(); //oops. Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode