Solution

The correct answer is A - III, B - I, C - II, D - IV

Key Points

• A. If the implementation of generated or derived classes differ only through a parameter we have - III. to use templates
  • Templates in C++ allow functions and classes to operate with generic types, enabling a higher degree of code reuse. If we have classes that differ only by the type of data they operate on, templates are an excellent way to optimize that.
• B. If the actual types of objects used cannot be known at compile time, then we have - I. to use class hierarchy
  • A class hierarchy allows us to use the principle of polymorphism where a base class reference can point to any derived class object. This feature is helpful when we don't know the exact type of objects at compile time.
• C. If inline operations are essential and templates are used then we have - II. improved run-time efficiency
  • Inline functions and templates can help improve runtime efficiency by eliminating the overhead of repeated function calls and allowing different data types to be handled by the same functions or classes.
• D. To gain access to differing instances for derived classes through base we have - IV. to use explicit casting
  • Casting allows us to convert one object type to another. To access the specific implementation of a derived class from something that is only aware of the base class, we would typically use casting. This allows us to recover the specific type of the derived class and access its specifics.