I would like to create a web site with many images. But I would like to protect against direct access to images, e.g. direct links to images without visiting the web site. What is the prefer...

Can we increase the re-usability for this key-oriented access-protection pattern: class SomeKey { friend class Foo; // more friends... ? SomeKey() {} // possibly non-copyable too }; class B...

Apparently this key-oriented access-protection pattern: class SomeKey { friend class Foo; SomeKey() {} // possibly non-copyable too }; class Bar { public: void protectedMethod(SomeKey); // ...