Kotlin Design Patterns: Simplifying the Prototype Pattern

We use the Prototype Pattern when creating new instances from scratch is more expensive than copying existing ones.

So, instead of instantiating new objects, you can have a prototype from which clones / copies are made.

Traditional Approach in Java:

In this Java example, GraphicElement represents a complex graphic element with complex initialization logic, such as loading textures, calculating geometry, etc.:

interface PrototypeCapable extends Cloneable {  
    PrototypeCapable clone() throws CloneNotSupportedException;  
}  

class GraphicElement implements PrototypeCapable {  
    private String color;  
    private List<String> points; // Represents complex geometry  
    private String texture;  
    // Getters and setters ommited.  

    public GraphicElement(String color, List<String> points, String texture) {  
        this.color = color;  
        this.points = points;
        this.texture = texture;
        if (this.texture == null) {
            this.texture = "Some complex initialization logic here (loading textures, calculating geometry, etc.)";
        }
}  

  @Override  
    public GraphicElement clone() throws CloneNotSupportedException {  
        return (GraphicElement) super.clone();  
    }  
} 

// Usage:  
List<String> initialPoints = Arrays.asList("x1", "y1", "x2", "y2");  
GraphicElement originalElement = new GraphicElement("Red", initialPoints, "BrickTexture");  
GraphicElement clonedElement = originalElement.clone();  
clonedElement.setColor("Blue");  
System.out.println("Cloned Element Color: " + clonedElement.getColor()); // Output: Blue

In this example, you can see cloning is used to create a new element clonedElement based on the existing originalElement, instead of instatiating a new object from scratch. Also, the color is changed from red to blue on the clonedElement.

Kotlin's Approach:

Kotlin allows for an efficient and concise way to implement cloning of complex objects.

data class GraphicElement(
    val color: String,
    val points: List<String>,
    var texture: String? = null,
) {
    init {
        if (texture == null) {
            texture = "Some complex initialization logic here (loading textures, calculating geometry, etc.)"
        }
    }
}

// Usage:
val initialPoints = listOf("x1", "y1", "x2", "y2")
val originalElement = GraphicElement("Red", initialPoints)
val clonedElement = originalElement.copy(color = "Blue") // Modifying color while cloning

In this Kotlin example, GraphicElement is a data class used for creating complex graphic elements. The copy method simplifies the process of cloning and modifying these elements.
Notice that the color for the clonedElement can be set / changed earlier, while copying the originalElement.

Kotlin Features Simplifying the Prototype Pattern

1. Data Classes: Offer an inbuilt copy method, streamlining the creation of prototype instances.
2. copy method: Allows changing specific properties while copying, allowing for more concise and expressive code.

Final Thougths

Kotlin's approach to the Prototype pattern showcases its efficiency and simplicity. Data classes and their built-in copy method make the cloning process straightforward, simplifying the pattern implementation while maintaining functionality.

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This article was originally posted to my Lucas Fugisawa on Kotlin blog, at: https://fugisawa.com/kotlin-design-patterns-simplifying-the-prototype-pattern/

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