construction error when template class derives from template class (gcc 4.1.1)

[seaswar]

I get the following error under gcc 4.1.1 but works fine under gcc
3.2.3. Is my construction not valid?

file tp.cpp:
template<template<typename> class>
class B { };

template<typename>
class C : public B<C> {
C() : B<C>() { } // line 6
};

$ g++ -c tp.cpp
tp.cpp: In constructor 'C< <template-parameter-1-1> >::C()':
tp.cpp:6: error: type/value mismatch at argument 1 in template
parameter list for 'template<template<class>
class<template-parameter-1-1> > class B'
tp.cpp:6: error: expected a class template, got 'C<
<template-parameter-1-1> >'

Thanks
Suresh

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[Radu]

seaswar wrote:
> I get the following error under gcc 4.1.1 but works fine under gcc
> 3.2.3. Is my construction not valid?
>
> file tp.cpp:
> template<template<typename> class>
> class B { };
>
> template<typename>
> class C : public B<C> {
> C() : B<C>() { } // line 6
> };
>
> $ g++ -c tp.cpp
> tp.cpp: In constructor 'C< <template-parameter-1-1> >::C()':
> tp.cpp:6: error: type/value mismatch at argument 1 in template
> parameter list for 'template<template<class>
> class<template-parameter-1-1> > class B'
> tp.cpp:6: error: expected a class template, got 'C<
> <template-parameter-1-1> >'
>

should be:

template<typename>
class C : public B<C> {

C() : B() { } // line 6
};

As a side note VC8 accepts C() : B<C>() w/o complain.

HTH
Radu

[marius lazer]

seaswar wrote:
> I get the following error under gcc 4.1.1 but works fine under gcc
> 3.2.3. Is my construction not valid?
>
> file tp.cpp:
> template<template<typename> class>
> class B { };
>
> template<typename>
> class C : public B<C> {
> C() : B<C>() { } // line 6
> };
>

The compiler is correct. Did you mean to use one of the following
constructs instead?

template<typename>
class B { };

template<template<typename> class T = B>
class C : public T<C<T> >
{
C() : T<C<T> >() {}
};

template<typename T>
class A : public B<A<T> >
{
A() : B<A<T> >() {}
};

Marius

[seaswar]

No. B is a class template that takes a template template parameter. C
is a class template (its template parameter is a typename; not a
template) that derives from B and passes itself as the template
argument to B. The problem occurs in the constructor of C. The compiler
thinks C is a class when it is clearly not. C is a class template (and
is a valid argument, IMO, for B's template parameter).

A work-around for this problem:

template<template<typename> class>
class B { };

template<typename>
class C;

typedef B<C> T;

template<typename>
class C : public T {
C() : T() { } // line 6
};

Sounds like a bug to me.
Suresh