Re: specialization bug

[Martin Sebor <sebor at roguewave dot com>]

Neil Radisch wrote:
> 
> I re-read my copy of the spec, and I believe I see what you mean,
> though paragraph 18 does not say what you quoted below.

No, that wasn't a quote, just a gist of the paragraph. It amounts to the
same thing (the "or" should have been "of").

> Anyhow, it seems that it becomes impossible to build the
> following program given the syntactical restriction
> (BTW the OLD_GCC_COMPILER constant refers
>   to 2.91 as opposed to the 2.95 I'm using on solaris)
> If you as me, the syntax bracketed by OLD_GCC_COMPILER
> makes alot more sense in this case. Or maybe there is
> something I still don't get.

Perhaps, but it's not allowed (if 2.91 accepts it then it's a bug).

> 
> class narf
> {
> private:
> 
>  template <class T> bool foo(T &v) const { return true; }
> #ifdef OLD_GCC_COMPILER
>  template <> bool foo(bool &v) { v = true; return false; }
> #endif
>  template <class T> bool gorp(T data) { return foo(data); }
> public:
> 
>  narf() {}
> 
>  void eat() { int i; gorp(i); }
>  void me() { bool b; gorp(b); }

This is not going to work either because of 14.7.3, p6:

-6- If a template, a member template or the member of a class template
is explicitly specialized then that specialization shall be declared
before the first use of that specialization that would cause an implicit
instantiation to take place, in every translation unit in which such a
use occurs; no diagnostic is required...

You'll have to define the member functions outside of the template and
after the definition of the explicit specialization.

Martin.

> };
> 
> #ifndef OLD_GCC_COMPILER
>  template <> bool narf::foo<bool>(bool &v) const { v = true; return false; }
> #endif
> 
> int main(int argc,char *argv[])
> {
> narf n;
> n.eat();
> n.me();
> 
>  return 0;
> }
> 
> ----- Original Message -----
> From: "Martin Sebor" <sebor@roguewave.com>
> To: "Neil Radisch" <nradisch@panix.com>
> Cc: <gcc-bugs@gcc.gnu.org>
> Sent: Monday, October 16, 2000 12:49 PM
> Subject: Re: specialization bug
> 
> > Neil Radisch wrote:
> > >
> > > gcc version - 2.95.2 19991024
> > > system type - sparc-sun-solaris2.6
> > > comand line - gcc ttest2.cpp -lstdc++
> > > compiler output:
> > > --------
> > > ttest2.cpp:8: explicit specialization in non-namespace scope `narf<C>'
> >
> > As the compiler says (in a not very helpful way), you can't declare an
> > explicit specialization in class scope. From 14.7.3, p2:
> >
> > -2- An explicit specialization shall be declared in the namespace of
> > which the template is a member, or, for member templates, in the
> > namespace of which the enclosing class or enclosing class template is a
> > member.
> >
> > There is no way to explicitly specialize a member template or a class
> > template without also explicitly specializing the enclosing template
> > (14.7.3, p18).
> >
> > Regards
> > Martin
> >
> > > ttest2.cpp:8: enclosing class templates are not explicitly specialized
> > > ttest2.cpp:8: syntax error before `{'
> > > ttest2.cpp:10: warning: all member functions in class `narf<C>' are
> > > private
> > > ttest2.cpp:10: semicolon missing after declaration of `narf<C>'
> > > ttest2.cpp:10: parse error at null character
> > > ttest2.cpp: In function `bool gorp()':
> > > ttest2.cpp:13: `mData' undeclared (first use this function)
> > > ttest2.cpp:13: (Each undeclared identifier is reported only once
> > > ttest2.cpp:13: for each function it appears in.)
> > > ttest2.cpp:13: implicit declaration of function `int foo(...)'
> > > ttest2.cpp: At top level:
> > > ttest2.cpp:14: parse error before `}'
> > > --------------------------------------------------
> > > preprocessed file:
> > > ------------------------------------------------
> > > # 1 "ttest2.cpp"
> > > template <class C> class narf
> > > {
> > > private:
> > >
> > >  C mData;
> > >
> > >  template <class T> bool foo(T &v) { return true; }
> > >  template <> bool foo(bool &v) { v = true; return false; }
> > >
> > > public:
> > >
> > >  narf() {}
> > >  bool gorp() { return foo(mData); }
> > > };
> > >
> > > int main(int argc,char *argv[])
> > > {
> > >  narf<int> i;
> > >  narf<bool> b;
> > >
> > >  return 0;
> > > }
> > > ---------------------------------------------------------------
> > >
> >
>   ------------------------------------------------------------------------
> > >                  Name: ttest2.cpp
> > >    ttest2.cpp    Type: unspecified type (application/octet-stream)
> > >              Encoding: quoted-printable
> >

-- 
==============================================
    Martin Sebor, Lead Software Engineer
C++ Standards Group, Rogue Wave Software, Inc.
    sebor@roguewave.com   (303) 545-3287