TXXXImplementation is a nontemplatized abstract base class that has methods for implementing the operations of the template. When the implementation methods need to perform a type-specific operation, they delegate to private pure virtual methods. The pure-virtual type-specific methods typically include deleting, copying, comparing, and streaming.
TXXX is a class template for a concrete class that privately inherits from TXXXImplementation. It has public methods that delegate to the TXXXImplementation implementation methods, and private virtual methods that implement the TXXXImplementation type-specific methods.