Classical Polymorphism and Generic Programming

The C++ standard library has two distinct, yet equally important, missions. One of these missions is to provide rock-solid implementations of certain concrete data types or functions that have tended to be useful in many different programs, yet aren't built into the core language syntax. This is why the standard library contains std::string, std::regex, std::filesystem::exists, and so on. The other mission of the standard library is to provide rock-solid implementations of widely used abstract algorithms such as sorting, searching, reversing, collating, and so on. In this first chapter, we will nail down exactly what we mean when we say that a particular piece of code is "abstract," and describe the two approaches that the standard library uses to provide abstraction: classical polymorphism and generic programming.

We will look at the following topics in this chapter:

• Concrete (monomorphic) functions, whose behavior is not parameterizable
• Classical polymorphism by means of base classes, virtual member functions, and inheritance
• Generic programming by means of concepts, requirements, and models
• The practical advantages and disadvantages of each approach