Item 25: Virtualizing constructors and non-member functions.(More Effective C++)

Consider what readComponent does. It creates a new object, either a TextBlock or a Graphic, depending on the data it reads. Because it creates new objects, it acts much like a constructor, but because it can create different types of objects, we call it a virtual constructor. A virtual constructor is a function that creates different types of objects depending on the input it is given. Virtual constructors are useful in many contexts, only one of which is reading object information from disk (or off a network connection or from a tape, etc.).

A particular kind of virtual constructor — the virtual copy constructor — is also widely useful. A virtual copy constructor returns a pointer to a new copy of the object invoking the function. Because of this behavior, virtual copy constructors are typically given names like copySelf, cloneSelf, or, as shown below, just plain clone.