Prototype.md

Prototype

Definition

Specify the kind of objects to create using a prototypical instance, and create new objects by copying this prototype.

Frequency of use:

Medium

---

UML class diagram

---

Participants

    The classes and objects participating in this pattern are:

• Prototype  (ColorPrototype)
  • declares an interface for cloning itself
• ConcretePrototype  (Color)
  • implements an operation for cloning itself
• Client  (ColorManager)
  • creates a new object by asking a prototype to clone itself

---

Structural code in C#

This structural code demonstrates the Prototype pattern in which new objects are created by copying pre-existing objects (prototypes) of the same class.

using System;
using System.Collections.Generic;

namespace DoFactory.GangOfFour.Builder.Structural
{
    /// <summary>
    /// MainApp startup class for Structural
    /// Builder Design Pattern.
    /// </summary>
    public class MainApp
    {
        /// <summary>
        /// Entry point into console application.
        /// </summary>
        public static void Main()
        {
            // Create director and builders
            Director director = new Director();

            Builder b1 = new ConcreteBuilder1();
            Builder b2 = new ConcreteBuilder2();

            // Construct two products
            director.Construct(b1);
            Product p1 = b1.GetResult();
            p1.Show();

            director.Construct(b2);
            Product p2 = b2.GetResult();
            p2.Show();

            // Wait for user
            Console.ReadKey();
        }
    }

    /// <summary>
    /// The 'Director' class
    /// </summary>
    class Director
    {
        // Builder uses a complex series of steps
        public void Construct(Builder builder)
        {
            builder.BuildPartA();
            builder.BuildPartB();
        }
    }

    /// <summary>
    /// The 'Builder' abstract class
    /// </summary>
    abstract class Builder
    {
        public abstract void BuildPartA();
        public abstract void BuildPartB();
        public abstract Product GetResult();
    }

    /// <summary>
    /// The 'ConcreteBuilder1' class
    /// </summary>
    class ConcreteBuilder1 : Builder
    {
        private Product _product = new Product();

        public override void BuildPartA()
        {
            _product.Add("PartA");
        }

        public override void BuildPartB()
        {
            _product.Add("PartB");
        }

        public override Product GetResult()
        {
            return _product;
        }
    }

    /// <summary>
    /// The 'ConcreteBuilder2' class
    /// </summary>
    class ConcreteBuilder2 : Builder
    {
        private Product _product = new Product();

        public override void BuildPartA()
        {
            _product.Add("PartX");
        }

        public override void BuildPartB()
        {
            _product.Add("PartY");
        }

        public override Product GetResult()
        {
            return _product;
        }
    }

    /// <summary>
    /// The 'Product' class
    /// </summary>
    class Product
    {
        private List<string> _parts = new List<string>();

        public void Add(string part)
        {
            _parts.Add(part);
        }

        public void Show()
        {
            Console.WriteLine("\nProduct Parts -------");
            foreach (string part in _parts)
                Console.WriteLine(part);
        }
    }
}

Output

Cloned: I\
Cloned: II