template specialization, nested?

[Schüle Daniel]

Hello all,

my question is basically wheather it's possible to
have nested templates .. I mean the following
if there are one templ. class and one global templ. function

is it possible to specialize the function for say <int>
but this for all possible classes (from class template)

the code is here

template <typename>
class X;

template <typename type>
void foo(X<type> &);

template <typename type = int>
class X
{
friend void foo<type>();
type x;
public:
X(type x) : x(x) {}
};

template <typename type>
void foo(X<type> & x)
{
cout << "with type = " << typeid(type).na me() << endl;
cout << x.x << endl;
}

template <> // this seems not ok
template <typename type> // but i need "type" for X
void foo<void>(X<typ e> & x)
{
cout << "this is void overload" << endl;
cout << x.x << endl;
}

int main()
{
X<> x(1); // int
foo<void>(x);
return EXIT_SUCCESS;
}

Regards, Daniel

g++ --version
g++ (GCC) 4.0.2

[Victor Bazarov]

Re: template specialization, nested?

Schüle Daniel wrote:[color=blue]
> my question is basically wheather it's possible to
> have nested templates .. I mean the following
> if there are one templ. class and one global templ. function
>
> is it possible to specialize the function for say <int>
> but this for all possible classes (from class template)[/color]

Uh... I am not sure I understand what you're trying to accomplish.
[color=blue]
>
> the code is here
>
> template <typename>
> class X;
>
> template <typename type>
> void foo(X<type> &);
>
> template <typename type = int>
> class X
> {
> friend void foo<type>();[/color]

There is no 'foo' without arguments! Did you mean

friend void foo<type>(X&);

?
[color=blue]
> type x;
> public:
> X(type x) : x(x) {}
> };
>
> template <typename type>
> void foo(X<type> & x)
> {
> cout << "with type = " << typeid(type).na me() << endl;
> cout << x.x << endl;
> }
>
> template <> // this seems not ok
> template <typename type> // but i need "type" for X[/color]

OK. So, you're trying to define a specialisation of 'foo' on 'void'
so that the argument is now a template. IOW, you're defining another
template here... That's not possible. Besides, there are no partial
specialisations of function templates.

Why do you think you need this construct?
[color=blue]
> void foo<void>(X<typ e> & x)
> {
> cout << "this is void overload" << endl;
> cout << x.x << endl;
> }
>
> int main()
> {
> X<> x(1); // int
> foo<void>(x);
> return EXIT_SUCCESS;
> }
>
> Regards, Daniel
>
> g++ --version
> g++ (GCC) 4.0.2
>[/color]

V
--
Please remove capital As from my address when replying by mail

[Schüle Daniel]

Re: template specialization, nested?

Hello Victor,
[color=blue][color=green]
>> template <typename>
>> class X;
>>
>> template <typename type>
>> void foo(X<type> &);
>>
>> template <typename type = int>
>> class X
>> {
>> friend void foo<type>();[/color]
>
>
> There is no 'foo' without arguments! Did you mean
>
> friend void foo<type>(X&);[/color]

yes, of course you are right
[color=blue][color=green]
>> type x;
>> public:
>> X(type x) : x(x) {}
>> };
>>
>> template <typename type>
>> void foo(X<type> & x)
>> {
>> cout << "with type = " << typeid(type).na me() << endl;
>> cout << x.x << endl;
>> }
>>
>> template <> // this seems not ok
>> template <typename type> // but i need "type" for X[/color]
>
>
> OK. So, you're trying to define a specialisation of 'foo' on 'void'
> so that the argument is now a template. IOW, you're defining another
> template here... That's not possible. Besides, there are no partial
> specialisations of function templates.[/color]

something like

template <typename type>
void foo() {}

template <>
void foo<int>(){}

my understanding of it is, that this is fully specialized
and is ok, my compiler at least doesn't complain
[color=blue]
> Why do you think you need this construct?[/color]
I thought it's time to get familar with template usage
(to write libraries)
so mostly this an academic case
[color=blue][color=green]
>> void foo<void>(X<typ e> & x)[/color][/color]

isn't it fully specialized?

Regards, Daniel

[Victor Bazarov]

Re: template specialization, nested?

Schüle Daniel wrote:[color=blue]
> [..]
> something like
>
> template <typename type>
> void foo() {}
>
> template <>
> void foo<int>(){}
>
> my understanding of it is, that this is fully specialized
> and is ok, my compiler at least doesn't complain[/color]

Yes. Fully specialised function templates are OK.
[color=blue][color=green]
>> Why do you think you need this construct?[/color]
> I thought it's time to get familar with template usage
> (to write libraries)
> so mostly this an academic case
>[color=green][color=darkred]
>>> void foo<void>(X<typ e> & x)[/color][/color]
>
> isn't it fully specialized?[/color]

How would it be if 'type' is unknown?

V
--
Please remove capital As from my address when replying by mail

[Schüle Daniel]

Re: template specialization, nested?

[..]
[color=blue][color=green][color=darkred]
>>>>void foo<void>(X<typ e> & x)[/color]
>>
>>isn't it fully specialized?[/color]
>
>
> How would it be if 'type' is unknown?[/color]

my minds eye saw only
void foo<void>
:)

thanks for correction