Re: Error:Template as friend class with different arguement list

From:
"Alf P. Steinbach" <alfps@start.no>
Newsgroups:
comp.lang.c++
Date:
Tue, 22 May 2007 08:49:10 +0200
Message-ID:
<5bfi3bF2sstitU1@mid.individual.net>
* neelsmail@rediffmail.com:

This works with MS VS 2003 --->

class B;
class C;
template <class B, class C> class A; //forward declaration

template <class DBT_>
class D {
public:
        friend class A<B,C>; //Error as B and C are not known as
template parameters
private :
        DBT_ f;

};


This doesn't make the template a friend, it makes the concrete class
A<B,C> a friend. In particular, A<int,int>, the only instantiation used
in the program, is not a friend of D.

template <typename b,typename c>
class A{
private:
        typedef D<typename b> myClass;


This is invalid syntax. Use just "b", not "typename b". Even though
MSVC may allow it, "typename" is not a kind spice that you can sprinkle
liberally everywhere in the hope of satisfying the compiler.

Use "typename" to inform the compiler that a dependent name denotes a type.

A dependent name is a name which definition depends on a template
parameter, e.g. Foo<b>::Type.

        myClass E;
        int j;

};

int func()
{

        A<int,int> a;
        return 0;
}


--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
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