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Let us consider the following nested templates case:

template<typename T>
class Outer{

public:
template<typename U>
class Inner{

public:
void f();
};

};

Then the following specialization
template<> template<typename U> void Outer<int>::Inner<U>::f(){};
results in compile-time error (I've tried to compile it with gcc 3.2.2)

main.cpp:XXX: invalid use of undefined type `class Outer<int>::Inner<U>'
main.cpp:XXX: declaration of `class Outer<int>::Inner<U>'
main.cpp:XXX: template definition of non-template `void
Outer<int>::Inner<U>::f()'

Can anyone help me to figure out the problem?

Thanks in advnace,
Andriy Shnyr

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On Wed, 3 Dec 2003 17:35:21 +0000 (UTC), (Andriy
Shnyr) wrote:

>Let us consider the following nested templates case:
>
>template<typename T>
>class Outer{
>
>public:
> template<typename U>
> class Inner{
>
> public:
> void f();
> };
>
>};
>
>Then the following specialization
>template<> template<typename U> void Outer<int>::Inner<U>::f(){};
>results in compile-time error (I've tried to compile it with gcc 3.2.2)
>
>main.cpp:XXX: invalid use of undefined type `class Outer<int>::Inner<U>'
>main.cpp:XXX: declaration of `class Outer<int>::Inner<U>'
>main.cpp:XXX: template definition of non-template `void
> Outer<int>::Inner<U>::f()'
>
>Can anyone help me to figure out the problem?
>
>Thanks in advnace,
>Andriy Shnyr
>
>---
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template < typename O >
struct outer
{
template < typename I >
struct inner
{
void f();
};
};

template <>
struct outer<int>
{
template < typename I >
struct Inner
{
void f();
};
};

Cheers!

"Andriy Shnyr" <> wrote...
> Let us consider the following nested templates case:
>
> template<typename T>
> class Outer{
>
> public:
> template<typename U>
> class Inner{
>
> public:
> void f();
> };
>
> };
>
> Then the following specialization
> template<> template<typename U> void Outer<int>::Inner<U>::f(){};
> results in compile-time error (I've tried to compile it with gcc 3.2.2)
>
> main.cpp:XXX: invalid use of undefined type `class Outer<int>::Inner<U>'
> main.cpp:XXX: declaration of `class Outer<int>::Inner<U>'
> main.cpp:XXX: template definition of non-template `void
> Outer<int>::Inner<U>::f()'
>
> Can anyone help me to figure out the problem?

If you need to specialise the outer class but keep the nested template
a template, you need to first declare the existence of 'Outer<int>::Inner'
template manually:

template<> class Outer<int> {
template<class U> class Inner {
public:
void f();
};
};

Otherwise you're declaring a member function of a class that doesn't
exist.

That's my take on it, anyway.

Victor

On 12/03/2003 11:35 AM, Andriy Shnyr wrote:
[snip]
> main.cpp:XXX: invalid use of undefined type `class Outer<int>::Inner<U>'
> main.cpp:XXX: declaration of `class Outer<int>::Inner<U>'
> main.cpp:XXX: template definition of non-template `void
> Outer<int>::Inner<U>::f()'
>
> Can anyone help me to figure out the problem?
IIRC, adding ::template Inner<U> solved the compile problem for me;
however, I found a problem with the produced code not selecting the
right specialization, as reported here:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13088

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