Ensuring constant correctness for a program

Although there is no formal definition, constant correctness means objects that are not supposed to be modified (are immutable) remain unmodified. As a developer, you can enforce this by using the const keyword for declaring parameters, variables, and member functions. In this recipe, we will explore the benefits of constant correctness and how to achieve it.

How to do it...

To ensure constant correctness for a program, you should always declare the following as constants:

• Parameters to functions that are not supposed to be modified within the function:

  struct session {};
  session connect(std::string const & uri,
                  int const timeout = 2000)
  {
    /* do something */
    return session { /* ... */ };
  }
  

• Class data members that do not change:

  class user_settings
  {
  public:
    int const min_update_interval = 15;
    /* other members */
  };
  

• Class member functions that do not...