Re: Declaring a template class with two template params a friend in a non-template class

From:
"Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 25 Aug 2010 09:25:51 +0200
Message-ID:
<i52gi4$9ai$1@news.eternal-september.org>
* A L, on 25.08.2010 08:17:

I have an abstract class:

class Attribute { /* ...*/ };

Now I have another class:

template<typename T, typename U>
class Mgr
{
     static U *create(const std::string k, std::string v)
     {
         static T *p = 0;
         if (!p)
         {
             p = new T();
         }


Above is unnecessary because C++ does it for you:

   static T *p = new T();

         T&r = *p;
         U *a = const_cast<U*>(r.get(k));


This const_cast seems pretty dangerous.

         return a;
     }
};

Both of these classes are declared/defined in different header files.

The problem is that the constructors of Attribute class are private so
I have to declare the Mgr class a friend of Attribute. That's what I
have a problem doing - I am having a difficult time with the template
syntax when it comes to declaring a template class (with two template
parameters) a friend in a non-template class - I am getting lots of
compilation errors on the friend template declaration. Can any kind
sole tell me how I am supposed to do it? Declare a template class with
two template parameters a friend in a non-template class???


Design Attribute as a singleton.

Cheers & hth.,

- Alf

--
blog at <url: http://alfps.wordpress.com>

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