c++/8858: Gcc "rebinds" template member names.

c++/8858: Gcc "rebinds" template member names.

[eivuokko]

>Number:         8858
>Category:       c++
>Synopsis:       Gcc "rebinds" template member names.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 07 06:36:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     eivuokko@bonumit.com
>Release:        gcc-3.2
>Organization:
>Environment:

(also tried with rc version of mingw-gcc 3.2.1)
C:\base\test>g++ -v
Reading specs from c:/devel/mingw/bin/../lib/gcc-lib/mingw32/3.2/specs
Configured with: ../gcc/configure --with-gcc --with-gnu-ld --with-gnu-as --host=
mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable
-languages=f77,c++,objc,ada --disable-win32-registry --disable-shared
Thread model: win32
gcc version 3.2 (mingw special 20020817-1)
>Description:
If you have type inside a template, issuing last template-id
as member of it rebinds the template instead of using previous type.

ie
typedef foo::bar<int>::bar<float> baz;
generates same effect as
typedef foo::bar<float> baz;
>How-To-Repeat:
example session, program asserts in unexpected place, it should assert before, for difffrent type.

C:\base\test>g++ gcc_rebind_bug.cpp -o gcc_rebind_bug -Wall && gcc_rebind_bug
Assertion failed: ( IsSame< cons<int, cons<char, cons<double,float> > >, test_ty
pe>::Value ), file gcc_rebind_bug.cpp, line 37
>Fix:
Haven't found one yet, except moving member template outside
the class.
>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="gcc_rebind_bug.cpp"
Content-Disposition: inline; filename="gcc_rebind_bug.cpp"

#include <cassert>

template<class T_, class U_> class cons {};

template<class L_> class list {
public:
    typedef L_ type;
    template<class T_> class add :
        public ::list< ::cons<T_, L_> > {};
} ;
    
template<class T1_,class T2_> class IsSame {
public:
    enum { Value = false } ;
} ;
    
template<class T_> class IsSame<T_,T_> {
public:
    enum { Value = true } ;
} ;


int main() {
    // assure IsSame works
    assert(( IsSame<int,int>::Value ));
    assert(( IsSame<float,float>::Value ));
    assert(( IsSame<cons<int,cons<char,float> >,cons<int,cons<char,float> > >::Value ));
    // real test
    typedef list<cons<double,float> >::add<char>::add<int>::type test_type;
    // this should absolutely fail
    assert(( IsSame<
        cons<int, cons<double,float> >,
        test_type>::Value ));
    // and this shouldn't
    assert(( IsSame<
        cons<int, cons<char, cons<double,float> > >,
        test_type>::Value ));
}

Re: c++/8858: Gcc "rebinds" template member names.

[bangerth]

Synopsis: Gcc "rebinds" template member names.

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Mon Dec  9 11:29:52 2002
State-Changed-Why:
    Confirmed. Very wicked template magic, though.
    
    Here's a slightly smaller testcase, failing in the wrong
    place:
    ----------------------------------#include <cassert>
    
    template<class T_, class U_> struct cons {};
    
    template<class L_> struct list {
        typedef L_ type;
        template<class T_> class add : public ::list< ::cons<T_, L_> > {};
    };
        
    template<class T1_,class T2_> struct IsSame        { enum { Value = false }; };
    template<class T_>            struct IsSame<T_,T_> { enum { Value = true } ; };
    
    
    int main() {
      typedef list<cons<double,float> >::add<char>::add<int>::type test_type;
                                       // this should absolutely fail
      assert((IsSame<cons<int, cons<double,float> >,
                     test_type>::Value ));
                                       // and this shouldn't
      assert(( IsSame<
               cons<int, cons<char, cons<double,float> > >,
               test_type>::Value ));
    }
    ------------------------------
    
    This never went right, at least not back to 2.95.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8858