New Story

Refactoring 017 - Convert Attributes to Sets

by Maximiliano ContieriOctober 21st, 2024

Too Long; Didn't Read

Using sets for attributes simplifies your code and makes state management easier

featured image - Refactoring 017 - Convert Attributes to Sets

Favor immutability by converting attributes to sets

TL;DR: Using sets for attributes simplifies your code and makes state management easier

Problems Addressed

Mutability
Complexity
Attributes become polluted
Setters

//gzht888.com/how-to-find-the-stinky-parts-of-your-code-part-vii-8dk31x0

//gzht888.com/how-to-find-the-stinky-parts-of-your-code-part-vi-cmj31om

Steps

Identify attributes representing states
Replace the attributes with sets: one for each state
Adjust methods to move items between sets instead of mutating attributes

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<Bill>;
  paidBills: Set<Bill>;

  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