Prototype pattern

The prototype pattern is a creational design pattern in software development. It is used when the types of objects to create is determined by a prototypical instance, which is cloned to produce new objects. This pattern is used to avoid subclasses of an object creator in the client application, like the factory method pattern does, and to avoid the inherent cost of creating a new object in the standard way (e.g., using the 'new' keyword) when it is prohibitively expensive for a given application.

To implement the pattern, the client declares an abstract base class that specifies a pure virtual clone() method. Any class that needs a "polymorphic constructor" capability derives itself from the abstract base class, and implements the clone() operation.

The client, instead of writing code that invokes the "new" operator on a hard-coded class name, calls the clone() method on the prototype, calls a factory method with a parameter designating the particular concrete derived class desired, or invokes the clone() method through some mechanism provided by another design pattern.

The mitotic division of a cell — resulting in two identical cells — is an example of a prototype that plays an active role in copying itself and thus, demonstrates the Prototype pattern. When a cell splits, two cells of identical genotype result. In other words, the cell clones itself.

Designs that make heavy use of the composite and decorator patterns often can benefit from Prototype as well.Maze::addRoom0x1160f50 Maze::addRoom0x1160f70 Room::setSide00x11613c0 Room::setSide20x1160f90 Room::setSide10x11613e0 Room::setSide30x1161400 Room::setSide00x1161420 Room::setSide20x1161440 Room::setSide10x1161460 Room::setSide30x1160f90

• Function prototype