Gabriel Dos Reis - Re: Char_traits (part 2+) (original) (raw)

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• From: Gabriel Dos Reis
• To: Benjamin Kosnik
• Cc: jack_reeves at hotmail dot com, libstdc++ at gcc dot gnu dot org
• Date: 16 Aug 2002 20:42:44 +0200
• Subject: Re: Char_traits (part 2+)
• Organization: CodeSourcery, LLC
• References: <F156GQvnbEG10Gai4om0000075f@hotmail.com> <20020816104914.5b79ec31.bkoz@redhat.com> <m31y8yhdyk.fsf@soliton.integrable-solutions.net> <20020816112732.1ccbc468.bkoz@redhat.com>

Benjamin Kosnik bkoz@redhat.com writes:

| > | typedef unsigned short unicode_type; | > | typedef unsigned char unsigned_type; | > | | > | then doing | > | | > | template<> struct std::char_traits | > | { | > | // do the work | > | } | > | | > | etc. Isn't this legal? | > | > No, it isn't. | | Ouch. Is it implementation-defined, or illegal?

It is undefined-behaviour since unicode_type is not a user-defined type.

| If it's | implementation-defined (or undefined behavior), then can can libstdc++ | "define" it to be ok for non-required types (all !(wchar_t || char))?

That would be a possible extension, but then we should be careful about the meaning we give it.

Sometime ago (one? two years), I was working on the char_traits<> thingy seeking for ways to provide points-of-customization for users -- but I gave up, being distracted by other things (and ironically enough, I ditched the patch from my disk two weeks ago :-(( )

| If not, then I don't see any clear way out of this mess.

Deprecate char_traits<> :-)

Seriously, we may try to define points-of-customization so that the primary template char_traits<> remains useful if some defnitions are provided by users. I don't know how that is better than just telling users that GCC won't reformate their hard drive if they do the specialization -- that however demands more typing.

-- Gaby

• Follow-Ups:
  • Re: Char_traits (part 2+)
    * From: Matt Austern
• References:
  • Char_traits (part 2+)
    * From: Jack Reeves
  • Re: Char_traits (part 2+)
    * From: Benjamin Kosnik
  • Re: Char_traits (part 2+)
    * From: Gabriel Dos Reis
  • Re: Char_traits (part 2+)
    * From: Benjamin Kosnik