calling a template class' template member function from a template function - c++

On Oct 26, 7:32 pm, Marian Ciobanu <ci...@inbox.com> wrote:

> Since both GCC and Comeau give errors at the same point, chances are
> that my code is wrong. If that's the case, I wonder how to make it
> right. Also, I wonder if it is right that uncommenting the line with
> the global "void f(int, float)" makes the errors go away.
>
> So here's the code:
>
> template <typename T>
> struct X
> {
> template <typename U> int f();
>
> };
>
> //template <typename T> void f(int, float); // any parameter(s) would do
>
> template <typename T>
> int g()
> {
> X<T> tmp;
> return tmp.f<int>(); // error
>
> }

The compiler needs some help in identifying a template specialization
inside another template specialization, such as f<int>() in this case:

template <typename T>
int g()
{
X<T> tmp;
return tmp.template f<int>(); // OK
}

Greg



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On 2007-10-27, Marian Ciobanu <ciobi@inbox.com> wrote:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>
> template <typename T>
> struct X
> {
> template <typename U> int f();
> };
>
> //template <typename T> void f(int, float); // any parameter(s) would do
>
> template <typename T>
> int g()
> {
> X<T> tmp;
> return tmp.f<int>(); // error
> }
>
><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

You are missing the keyword "template" here:
return tmp.template f<int>();

tmp is of a dependent type X<T> with T a template parameter of this
template. This means that you need to use the template keyword to
have f considered to be a member template.


>
> There's no need for an instantiation of g().
>
> What I find rather puzzling is that uncommenting the line with the
> global template function "f" makes everything compile with GCC and
> Comeau. While this takes care of my problem, I suspect that it's not
> supposed to. So: what happens here and what should be happening?

It is puzzling(!) but it's definitely not the right fix. :-)


--
Charles Bailey
http://ccgi.hashpling.plus.com/blog/

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* Marian Ciobanu:
>
> template <typename T>
> struct X
> {
> template <typename U> int f();
> };
>
> //template <typename T> void f(int, float); // any parameter(s) would do
>
> template <typename T>
> int g()
> {
> X<T> tmp;
> return tmp.f<int>(); // error
> }

What f is or isn't depends on the template parameter T.

You must inform the compiler about what you assume f to be.

return tmp.template f<int>();


Cheers, & hth.,

- Alf

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