Prototype Design Pattern in R

1. Definition

The Prototype Design Pattern involves creating objects by copying an existing object, the prototype. It allows the addition of any subclass instance of a known superclass at runtime.

2. Problem Statement

Imagine you're developing a graphic editor in R. Each shape in the editor, like a circle or a rectangle, is an object. When you want to duplicate a shape, you don't want to go through the initialization process again, especially if it's computationally expensive or involves fetching data. How can you efficiently create a copy of an existing object?

3. Solution

Use the Prototype pattern. Instead of creating a new instance from scratch, clone an existing instance. The object that you're copying is the prototype. It provides an interface for cloning itself.

4. Real-World Use Cases

1. Graphic editors where objects can be duplicated.

2. In games, where players, monsters, or other entities can be cloned.

3. When objects have numerous shared configurations and only a few differences.

5. Implementation Steps

1. Create a prototype interface that includes a method for cloning itself.

2. Concrete classes implement this interface by returning a copy of themselves.

3. Use the clone method to duplicate objects.

6. Implementation in R Programming

# Step 1: Prototype interface
Prototype <- function() {
  list(
    clone = function() {
      stop("Abstract method. Implement in concrete prototypes.")
    }
  )
}
# Step 2: Concrete prototypes
Circle <- function(radius) {
  shape <- Prototype()
  shape$radius <- radius
  shape$clone <- function() {
    return(Circle(shape$radius))
  }
  return(shape)
}
Rectangle <- function(width, height) {
  shape <- Prototype()
  shape$width <- width
  shape$height <- height
  shape$clone <- function() {
    return(Rectangle(shape$width, shape$height))
  }
  return(shape)
}
# Step 3: Client code
originalCircle <- Circle(5)
clonedCircle <- originalCircle$clone()
originalRectangle <- Rectangle(4, 7)
clonedRectangle <- originalRectangle$clone()
list(originalCircle = originalCircle, clonedCircle = clonedCircle,
     originalRectangle = originalRectangle, clonedRectangle = clonedRectangle)

Output:

$originalCircle
$originalCircle$radius
[1] 5
$clonedCircle
$clonedCircle$radius
[1] 5
$originalRectangle
$originalRectangle$width
[1] 4
$originalRectangle$height
[1] 7
$clonedRectangle
$clonedRectangle$width
[1] 4
$clonedRectangle$height
[1] 7

Explanation:

The Prototype Design Pattern here allows us to clone complex objects without going through the object's initialization.

1. We started with the Prototype interface that provides a method for cloning.

2. Two concrete prototypes, Circle and Rectangle, implemented the prototype interface. They provided their definitions for the clone method to return copies of themselves.

3. The client code created instances of these shapes and then cloned them using their clone method. The results show that the original and cloned objects have the same properties, verifying the duplication process.

Using the prototype pattern, the cloning operation becomes straightforward and efficient, avoiding the need for complex initialization in the duplication process.

7. When to use?

Use the Prototype Pattern when:

1. Classes to instantiate are specified at runtime, making a factory pattern complex to implement.

2. Objects have numerous shared configurations and differ slightly from one to another.

3. You want to avoid building a class hierarchy of factories that parallels the class hierarchy of products.

4. Instances of a class can have one of only a few different combinations of state.

This pattern helps keep the system flexible and efficient but can become complex if the objects being cloned have deep nested references or if there's a need to control the cloning process.