Prototype Design Pattern in Kotlin

1. Definition

The Prototype Design Pattern involves creating objects based on a template of an existing object through cloning. Instead of creating a new instance from scratch, an existing instance is copied.

2. Problem Statement

Imagine you're developing a video game that has certain characters. Each character has unique attributes, skills, and weapons. When a new level is unlocked, or when a player opts to use the same character in a different scenario, it's inefficient to create a completely new character from scratch. Moreover, initializing and setting up the character each time can be error-prone.

3. Solution

The Prototype pattern provides a mechanism to clone an existing object and then modify it as needed, instead of creating it from scratch. This pattern uses a prototypical instance and creates new objects by copying this prototype.

4. Real-World Use Cases

1. Spawning new game characters with similar attributes.

2. Creating consistent UI components in design software.

3. Cloning data structures for parallel processing.

5. Implementation Steps

1. Create a prototype interface that declares a cloning method.

2. Implement the prototype in concrete classes.

3. Use the prototype to clone and produce new objects.

6. Implementation in Kotlin Programming

// Prototype interface
interface GameCharacterPrototype {
    fun clone(): GameCharacterPrototype
}
// Concrete class implementing the Prototype
data class GameCharacter(val name: String, val weapon: String, val level: Int) : GameCharacterPrototype {
    override fun clone(): GameCharacterPrototype {
        return copy()
    }
}
fun main() {
    // Original character
    val originalCharacter = GameCharacter("Knight", "Sword", 5)
    // Cloning the character
    val clonedCharacter = originalCharacter.clone() as GameCharacter
    println("Original Character: $originalCharacter")
    println("Cloned Character: $clonedCharacter")
}

Output:

Original Character: GameCharacter(name=Knight, weapon=Sword, level=5)
Cloned Character: GameCharacter(name=Knight, weapon=Sword, level=5)

Explanation:

1. GameCharacterPrototype is the prototype interface that declares a clone method.

2. GameCharacter is a concrete class implementing this interface. The data class in Kotlin has a built-in copy method that fits perfectly with the prototype pattern, making cloning easier.

3. In the main function, an original game character is created. Later, the character is cloned using the clone method.

7. One More Example

Problem Statement

Consider you're developing a word processing software. This software has multiple templates for different types of documents like letters, resumes, reports, etc. Each template has a specific format, style, and default content. Creating a new instance of these templates every time from scratch is not efficient, especially when only a few details differ.

Solution

Use the Prototype pattern to clone an existing template and then customize it according to the user's requirements. This avoids the overhead and potential errors associated with creating templates from scratch every time.

Implementation Steps

1. Define a prototype interface that includes a method for cloning objects.

2. Implement the prototype in concrete classes.

3. Use the prototype instance to clone and produce new objects as needed.

Implementation in Kotlin Programming

// Prototype interface
interface DocumentPrototype {
    fun clone(): DocumentPrototype
}
// Concrete class implementing the Prototype
data class DocumentTemplate(val format: String, val defaultContent: String) : DocumentPrototype {
    override fun clone(): DocumentPrototype {
        return copy()
    }
}
fun main() {
    // Original document template
    val originalTemplate = DocumentTemplate("Letter Format", "Dear [Recipient Name],\n\n[Your Message]\n\nSincerely,\n[Your Name]")
    // Cloning the template
    val customizedTemplate = originalTemplate.clone() as DocumentTemplate
    println("Original Template Content: ${originalTemplate.defaultContent}")
    println("Customized Template Content: ${customizedTemplate.defaultContent}")
}

Output:

Original Template Content: Dear [Recipient Name],
[Your Message]
Sincerely,
[Your Name]
Customized Template Content: Dear [Recipient Name],
[Your Message]
Sincerely,
[Your Name]

Explanation:

1. DocumentPrototype is the prototype interface that has a clone method.

2. DocumentTemplate is a concrete class that represents the actual document templates. Kotlin's data class provides a copy method that is utilized for cloning.

3. In the main function, a basic letter template is created. It's then cloned using the clone method. For demonstration purposes, the cloned template isn't altered, but in a real-world scenario, this would be where customization happens.

7. When to use?

The Prototype pattern is useful when:

1. Objects have numerous shared configurations and only a few differences.

2. Creating a new instance of an object is more expensive or resource-intensive than copying an existing one.

3. Objects are required that are similar to existing objects.