For this recipe, you should be familiar with how to define and use function pointers.

To exemplify how std::invoke() can be used in different contexts, we will use the following function and class:

    int add(int const a, int const b) 
    { 
      return a + b; 
    } 

    struct foo 
    { 
      int x = 0; 

      void increment_by(int const n) { x += n; } 
    };