Advanced policy-based design
The techniques we have introduced in the previous section form the foundation of policy-based design - policies can be classes, template instantiations, or templates (used by template template parameters). The policy classes can be composed, inherited, or used statically at compile time. If a policy needs to know the type of the primary policy-based class, the CRTP can be used. The rest is largely variations on the same theme, as well as tricky ways to combine several techniques to accomplish something new. We will now consider some of these more advanced techniques.
Policies for constructors
Policies can be used to customize almost any aspect of the implementation, as well as to alter the class interface. However, there are unique challenges that arise when we attempt to customize class constructors using policies.
As an example, let’s consider another limitation of our current smart pointer. As it stands so far, the object owned by the...
