Define a Good Interface in C++

In C++, there is no keyword interface or protocol to define something what should conform to specific set of rules. But, it doesn't mean we can't express the concept with available tools. C++ has virtual member-function what enables polymorphic behavior and inheritance to share common code across related types.

Here's an example how to define a good interface:

struct LoginSession {
  int last_time_active;
};

class Account {
public:
  virtual ~Account() = default;

  virtual std::vector<LoginSession> FetchLoginSessions(
    int since) const = 0;
};

The interface has the following properties:

• does NOT declare any fields

• defines default virtual destructor

• does NOT contain any user-defined implementations

• does NOT use interface in its name

Let's figure out each point one-by-one (to be continued…)