[Bug c++/15534] New: Fails to inherit types from base class

[Bug c++/15534] New: Fails to inherit types from base class

[igodard at pacbell dot net]

In the source at the point of the first error messages:
    typedef
    typename std::allocator<T>::size_type st1;
    typedef
    typename size_type  st;
    typedef
    size_type   st2;
the first typedef works but the second two do not even though the class is derived from std::allocator<T>. In simple cases, e.g.:class A{
public:
    typedef
    int B;
    };

class C : public A {
public:
    B b;
    };

the derived class can inherit the types of the base class, but not here. Sticking in a "typename" doesn't help.

-- 
           Summary: Fails to inherit types from base class
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: igodard at pacbell dot net
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15534

[Bug c++/15534] Fails to inherit types from base class

[igodard at pacbell dot net]

------- Additional Comments From igodard at pacbell dot net  2004-05-19 03:04 -------
Created an attachment (id=6334)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=6334&action=view)
Compiler output (-v -save-temps)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15534

[Bug c++/15534] Fails to inherit types from base class

[igodard at pacbell dot net]

------- Additional Comments From igodard at pacbell dot net  2004-05-19 03:06 -------
Created an attachment (id=6335)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=6335&action=view)
Source code (-save-temps)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15534

[Bug c++/15534] Fails to inherit types from base class

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-19 03:12 -------
This is equivent to:
template <class T> class A
{
  typedef int t;
};

template <class T> class B: A<T>
{
  typedef t t1;
};

Which is invalid as t is not dependent so it needs to be declare not in the subclasses.
The fix would be to declare t1 as "typedef A<T>::t t1;"

Also one the mainline I get the following note:
pr15534.ii:31253: error: `size_type' does not name a type
pr15534.ii:31253: note: (perhaps `typename std::allocator<_CharT>::size_type' was intended)

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15534

[Bug c++/15534] Fails to inherit types from base class

[igodard at pacbell dot net]

------- Additional Comments From igodard at pacbell dot net  2004-05-19 09:30 -------
Comment three says the original example was invalid:
"Which is invalid as t is not dependent so it needs to be declare not in the subclasses". So here is a different example where "t" *is* dependent, and it fails too.

template <class T> class A
{
typedef T* t;
};

template <class T> class B: A<T>
{
typedef t t1;
};

or am I not understanding what you mean by dependent?

g++3.4.0 gives:
foo.cc:8: error: `t' does not name a type
foo.cc:8: error: (perhaps `typename A<T>::t' was intended)

Ivan

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15534

[Bug c++/15534] Fails to inherit types from base class

[pinskia at gcc dot gnu dot org]

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------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-19 11:16 -------
You misunderstand. 

Type-dependent expressions (From 14.6.2.2 P3):

Anid-expressionis type-dependent if it contains: 
—an identifier that was declared with a dependent type,
—a template-id that is dependent,
—a conversion-function-id that specifies a dependent type,
—a nested-name-specifier that contains a class-name that names a dependent type. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15534

[Bug c++/15534] Fails to inherit types from base class

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-05-19 13:42 -------
In your example, 
------ 
template <class T> class B: A<T> 
{ 
typedef t t1; 
}; 
------ 
you reference the name 't'. Since 't' does not depend on the template 
argument 'T', it is non-dependent and needs to be looked up at the 
time of declaration of the template. However, since name lookup does 
not look into template dependent base classes such as A<T> it doesn't 
find anything. The solution is to make sure that 't' is qualified as 
dependent, for example by writing 'typename A<T>::t'. 
 
This is really no different than all the other name lookup things that 
we believe are well-documented in the non-bugs and changes-in-3.4 sections 
of our web pages. Please review these if you are unsure. 
 
W. 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15534