How to have static data members in a header-only library?

Question

What is the best way to have a static member in a non-templated library class, without placing the burden of defining the member on the class user?

Say I want to pro

Answer 1

My own solution is to use a templated holder class, as static members work fine in templates, and use this holder as a base class.

template 
struct static_holder
{
    static T static_resource_;
};

template 
T static_holder::static_resource_;

Now use the holder class:

class expensive_resource { /*...*/ };

class i_want_a_static_member : private static_holder
{
public:
    void foo()
    {
        static_resource_.bar();
    }
};

But as the name of the member is specified in the holder class, you can't use the same holder for more than one static member.