Re: Template type parameters as friends in gcc

Hey all,

So I have a template class whose only template parameter is a type that
the class is to manage. It's actually an implementation of the common
Singleton design pattern. The class looks like this:

    template< class Type >
    class Singleton
    {
    public:
            static Type& instance();
    private:
            static Type* _instance;
    };

The instance() method looks like this:

    Type& Singleton::instance()
    {
        if( _instance == NULL )
        {
            _instance = new Type();
        }
        return *_instance;
    }

So, if I wanted to make a singleton class, it would just have to inherit
from this template class like so:

    class Tableau : public Singleton< Tableau >
    {
    private:
        // Make the constructor private so other parts of the
        // code can't create a new instance
        Tableau();

        // Make the Singleton class a friend so that it can
        // create the static instance of this guy.
        friend Singleton< Tableau >;
    };

This all works fine with MS Visual C++ .Net. This also used to work with
gcc. However, I tried to compile this with gcc 3.4.4 for cygwin, and no
go. I get the following error.

tableau.h:35: error: a class-key must be used when declaring a friend

A quick google for that error message and I see that newer versions of
gcc do not allow these so-called "ill-formed type" to be friends.
However, I can't find a fix or a work-around for this.

So, can anyone suggest a way to make make my singleton template more
platform-independent?

Thanks.

Dave