[boost] [Survey] utf8_codecvt_facet::do_length parameter

Subject: [boost] [Survey] utf8_codecvt_facet::do_length parameter
From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2012-06-28 11:30:14

There's some confusion in boost (and in various standard libraries) as to the declaration of 
        std::codecvt<>::do_length

The '03 and '11 standards say:
> 	template <class internT, class externT, class stateT>
> 	class codecvt : public locale::facet, public codecvt_base {
> 	// blah blah blah
> 		virtual int do_length(stateT&, const externT* from, const externT* end, size_t max) const;
> 	};

But some standard libraries (notably older Dinkumware libraries, and Visual C++ before Visual Studio11) say:
> 	virtual int do_length(const stateT&, const externT* from, const externT* end, size_t max) const;
(the first parameter is a const reference)

There's some preprocessor stuff to deal with this in boost/detail/utf8_codecvt_facet.hpp, but it's wrong:

> #if !defined(__MSL_CPP__) && !defined(__LIBCOMO__) \
>     && !defined(_LIBCPP_VERSION)
>     #define BOOST_CODECVT_DO_LENGTH_CONST const
> #else
>     #define BOOST_CODECVT_DO_LENGTH_CONST
> #endif
> 
>     virtual int do_length(
>         BOOST_CODECVT_DO_LENGTH_CONST std::mbstate_t &,
>         const char * from,
>         const char * from_end, 
>         std::size_t max_limit
> #if BOOST_WORKAROUND(__IBMCPP__, BOOST_TESTED_AT(600))
>         ) const throw();
> #else
>         ) const;
> #endif

I'm happy to fix this, but I'd like to be sure which systems actually have const parameters.

I've checked gcc and libc++, and they match the standard.
STL assures me that all versions of Visual Studio before VS11 do not match, but VS11 does.
The #defines above suggest to me that LibCOMO has this problem as well.
Does anyone have access to such an install?

And if anyone's standard library (that I haven't listed) does define the first parameter to std::codecvt<>::do_length as a const reference, please let me know.

Thanks!

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists_at_[hidden]>

A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
        -- Yu Suzuki