Prototype

Prototype

Prototype pattern refers to creating duplicate object while keeping performance in mind.

Problem

• Creating an instance is either expensive or complicated

Solution

• Make new instances by copying existing instances (clone)
• De-serialize when you need deep copies

Common Structure

• Prototype (Shape)
  • declares an interface for cloning itself
• ConcretePrototype (Circle, Square)
  • implements an operation for cloning itself
• Client (ShapeManager)
  • creates a new object by asking a prototype to clone itself.

Questions:

1. Should clonable interface be implemented?
2. What return type (Super class or concrete class) should the clone method have?

Collaborations

A client asks a prototype to clone itself.

Benefits

• Adding and removing objects (clones of ConcretePrototype) at run-time.
• Hides the complexities of making new instances from the client.
• Specifying new objects by varying values.
  • Highly dynamic systems let you define new behavior through object composition - by specifying values for an object's variables.
• In some circumstances, copying an object can be more efficient than creating a new object.

Drawbacks

• Making a copy of an object can sometimes be complicated and error-prone.

Definition

publicabstractclassShape{publicintId{get;set;}publicstringType{get;}protectedShape(stringtype){Type=type;}publicabstractShapeClone();}

publicclassCircle:Shape{publicCircle():base("Circle"){}// The MemberwiseClone method creates a shallow copy by creating a new object.// Thenand it copies the nonstatic fields of the current object to the new object.// If a field is a value type, a bit-by-bit copy of the field is performed. // If a field is a reference type, the reference is copied but the referred object is not.// Therefore, the original object and its clone refer to the same object.publicoverrideShapeClone(){return(Shape)this.MemberwiseClone();}}publicclassSquare:Shape{publicSquare():base("Square"){}publicoverrideShapeClone(){return(Shape)this.MemberwiseClone();}}

classShapeManager{publicstaticShapeGetShape(stringkey){returnShapes[key].Clone();}}

Usage

ShapeManager.LoadShapes();ShapeclonedCircle=ShapeManager.GetShape("Circle");Console.WriteLine(clonedCircle);ShapeclonedCircle2=ShapeManager.GetShape("Circle");Console.WriteLine(clonedCircle2);ShapecloneSquare=ShapeManager.GetShape("Square");Console.WriteLine(cloneSquare);

Output

Shape: 1 - Circle@46104728
Shape: 1 - Circle@12289376
Shape: 2 - Square@43495525

Relations with Other Patterns

• AbstractFactory and Prototype are competing patterns. However, they can be used together as well. An AbstractFactory might store a set of prototypes from which to clone and return product objects.

• Composite, Decorator - Prototype would allow to clone complex structures, instead of re-structuring them from scratch.