An abstract class typically doesn't need a user-written constructor

Reason

An abstract class typically does not have any data for a constructor to initialize.

Example

class Shape {
public:
    // no user-written constructor needed in abstract base class
    virtual Point center() const = 0;    // pure virtual
    virtual void move(Point to) = 0;
    // ... more pure virtual functions ...
    virtual ~Shape() {}                 // destructor
};

class Circle : public Shape {
public:
    Circle(Point p, int rad);           // constructor in derived class
    Point center() const override { return x; }
};

Exception

(e.g., use statistics data, debug information, etc.); such classes tend to have constructors. But be warned: Such classes also tend to be prone to requiring virtual inheritance.

• A base class constructor that does work, such as registering an object somewhere, might need a constructor.
• In extremely rare cases, you might find it reasonable for an abstract class to have a bit of data shared by all derived classes

Enforcement

Flag abstract classes with constructors.