#Prototype

#Overview

Create new objects by copying an existing instance (the prototype).

#When to use

• Object creation is expensive or complex.
• You need many similar instances with small variations.

#Java example

class Report implements Cloneable {
    private String title;
    private List<String> sections;

    Report(String title, List<String> sections) {
        this.title = title;
        this.sections = new ArrayList<>(sections);
    }

    public Report copy() {
        return new Report(title, sections);
    }
}

#TypeScript example

type Report = {
  title: string;
  sections: string[];
};

const prototype: Report = { title: "Monthly", sections: ["Summary", "KPIs"] };
const copy: Report = { ...prototype, sections: [...prototype.sections] };

#Pros and cons

Pros:

• Fast creation via cloning.
• Avoids complex constructor logic.

Cons:

• Deep copy can be tricky.
• Clones may share mutable state if not careful.

#Common pitfalls

• Shallow copy of nested objects.
• Mutating shared references after cloning.

#Related patterns

• Builder
• Factory Method