Prototype Pattern

• Create new objects by copying an existing object

Structure

Scenario

• In PowerPoint, add any shape, right click and duplicate

Problem Code

public interface IComponent
{
    void Render();
}
public class Circle : IComponent
{
    public int Radius { get; set; }

    public void Render()
    {
        Console.WriteLine("Rendering a Circle");
    }
}
public class ContextMenu
{
    public void Duplicate(IComponent component)
    {
        if (component is Circle)
        {
            Circle source = (Circle)component;
            Circle target = new Circle();
            target.Radius = source.Radius;
            //Add target to document
        }
    }
}

• Violates open closed principle, every time you add new shape, you need to modify the duplicate method
• Coupling between ContextMenu and Circle. ContextMenu needs to know about all shapes and details

Solution

• Move the logic for duplicating the circle from ContextMenu to Circle. Define clone method in circle
• Add clone to Component Interface
• Decouple the ContextMenu from Circle and make it talk to the Component interface

public interface IComponent
{
    void Render();
    IComponent Clone();
}
public class Circle : IComponent
{
    public int Radius { get; set; }

    public IComponent Clone()
    {
        Circle newCircle = new Circle();
        newCircle.Radius = Radius;
        return newCircle;
    }

    public void Render()
    {
        Console.WriteLine("Rendering a Circle");
    }
}
public class ContextMenu
{
    public void Duplicate(IComponent component)
    {
        IComponent newComponent = component.Clone();
        //Add target to document
    }
}

Example Structure

Example Code