What are some uses of template template parameters?

Question

I\'ve seen some examples of C++ using template template parameters (that is templates which take templates as parameters) to do policy-based class design. What other uses do

Answer 1

Here's one generalized from something I just used. I'm posting it since it's a very simple example, and it demonstrates a practical use case along with default arguments:

#include 

template  class Alloc final { /*...*/ };

template