From: "Yuval Ronen" <ronen_yuval@yahoo.com>
Terje Slettebø wrote:
I've brought this thread to Kevlin Henney's attention, as I've tended to take care of lexical_cast related questions on the list (including forwarding things needing his consideration, such as any changes to lexical_cast, to him). I'm replying here to let you know that your report is being taken care of.
Many, many thanks!
1. lexical_cast(Source arg) takes the source argument by value. Why not by const& ? Calling lexical_cast(some_basic_string) now makes a copy of the source argument for no reason.
I heard from Kevlin that the reason was that there originally were some issues with binding to string literals. Changing it to use const reference in my local copy still gives a lot of error messages, having to do with std::numeric_limits being used in the implementation. If we find a way to fix this (yet letting it still work on compilers with no class template partial specialisation, like MSVC 6), without breaking existing
then apparently, this change should be ok. If anyone makes a patch for
Thanks, yourself. :) Feedback is always welcome (regardless who's library it is); it's an opportunity to improve it. programs, this,
it would be welcome.
Hmmm, interesting. I'll give it a look. Maybe I'll be lucky enough to think of something...
I've been looking at this, as well, and after trying one approach (doing a compile-time switch to select between the ordinary, and a "dummy" std::numeric_limits (if the source type is an array)), I bumped into another problem: the specialisations for wchar_t, which assumes "const wchar_t *", not "const wchar_t[...]". This might again be fixed, using partial specialisation, to work with array, but another approach could be to "go back to square one" and do the array-to-pointer decay "manually": template<typename Target, typename Source> Target lexical_cast(const Source &arg) { // Array-to-pointer decay typedef typename mpl::if_< is_array<Source>, add_pointer<add_const<remove_bounds<Source>::type>::type>::type, Source >::type NewSource; detail::lexical_stream<Target, NewSource> interpreter; Target result; if(!(interpreter << arg && interpreter >> result)) throw_exception(bad_lexical_cast(typeid(NewSource), typeid(Target))); return result; } This passes all tests on Intel C++ 7.1, MSVC 7.1 and g++ 3.2. I've sent it as a suggestion to Kevlin, as well, I think he's pretty busy with other things. Anyone having a better suggestion than the above is of course welcome to contribute it. One thing about the above change is that it requires a few more includes, but this is really the simplest way I found to be able to use pass by const reference for lexical_cast. The additional includes are: #include <boost/type_traits/is_array.hpp> #include <boost/type_traits/remove_bounds.hpp> #include <boost/type_traits/add_pointer.hpp> #include <boost/type_traits/add_const.hpp> #include <boost/mpl/if.hpp> Regards, Terje