Sample Code Before class Bill { amount: number; paid: boolean; constructor(amount: number) { this.amount = amount; this.paid = false; } pay() { if (!this.paid) { this.paid = true; } } } const bill = new Bill(100); console.log(bill.paid); // false bill.pay(); console.log(bill.paid); // true After // 1. Identify attributes representing states class Accountant { // 2. Replace the attributes with sets: one for each state unpaidBills: Set; paidBills: Set; constructor() { this.unpaidBills = new Set(); this.paidBills = new Set(); } addBill(bill: Bill) { this.unpaidBills.add(bill); } payBill(bill: Bill) { // 3. Adjust methods to move items // between sets instead of mutating attributes if (this.unpaidBills.has(bill)) { this.unpaidBills.delete(bill); this.paidBills.add(bill); } } } class Bill { amount: number; constructor(amount: number) { this.amount = amount; } } const bill = new Bill(100); const accountant = new Accountant(); manager.addBill(bill); console.log(accountant.unpaidBills.has(bill)); // true manager.payBill(bill); console.log(accountant.paidBills.has(bill)); // true Type

[x] Semi-Automatic

Safety

This refactoring is safe when your attributes don't rely on specific indexing behavior.

\ Since sets don't maintain element order, check if your logic depends on order.

Why is the code better?

Entities are immutable in the essence.

\ Using sets ensures uniqueness and simplifies logic.

\ You no longer need to check for duplicates before adding elements.

\ Operations like union, intersection, and difference become straightforward, making your code more maintainable and flexible.

Limitations

Sets don't preserve element order.

\ If your logic depends on sequence, converting to a set may not be appropriate and you should use an Ordered Collection or Array

AI Refactoring

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| Without Proper Instructions | With Specific Instructions | |----|----| | ChatGPT | ChatGPT | | Claude | Claude | | Perplexity | Perplexity | | Copilot | Copilot | | Gemini | Gemini |