mcsee

// user-api-v1.json - Version 1 (maintained)
{
  "id": 317,
  "name": "Mr Nimbus",
  "email": "[email protected]",
  "nationalities": "Brazilian,Canadian,Oceanic"
}

// user-api-v2.json - Version 2 
// (new structure, backward compatible)

mcsee

// user-api-v1.json - Original API response
{
  "id": 317,
  "name": "Mr Nimbus",
  "email": "[email protected]",
  "nationalities": "Brazilian,Canadian,Oceanic"
}

// Later changed to this without versioning:
{

mcsee

use axum::{
  http::StatusCode,
  response::Json,
  routing::post,
  Router,
};
use serde_json::{json, Value};

async fn process_payment(
  Json(payload): Json<Value>

mcsee

use axum::{
  http::StatusCode,
  response::Json,
  routing::post,
  Router,
};
use serde_json::{json, Value};

async fn process_payment(
  Json(payload): Json<Value>

mcsee

public class ShoppingCart {
    private final List<Item> items = new ArrayList<>();
  
    // This version uses Optionals
    // Not all programming languages support this feature
    private Optional<Coupon> coupon = Optional.empty();

    public void addItem(Item item) {
        items.add(item);
    }

mcsee

public class ShoppingCart {
  private List<Item> items = new ArrayList<>();
    
  // 1. Identify nullable optional attributes
  // that could be collections
  // 2. Replace single nullable objects with empty collections
  private List<Coupon> coupons = new ArrayList<>();
    
  public void addItem(Item item) {
      this.items.add(item);

mcsee

public class ShoppingCart {
    private List<Item> items = new ArrayList<>();
    private Coupon coupon = null;
    
    public void addItem(Item item) {
        this.items.add(item);
    }
    
    public void redeemCoupon(Coupon coupon) {
        this.coupon = coupon;

mcsee

class InvoiceProcessor:
    def __init__(self, billing_ledger):
        self.billing_ledger = billing_ledger
    
    def process_invoice(self, customer, amount):
        # Pure business logic with proper domain objects
        if customer.credit_limit < amount:
            raise CreditLimitExceededException()
        
        # Business calculations

mcsee

class InvoiceProcessor:
    def process_invoice(self, invoice_data, database):
        # Business logic mixed with database access
        customer = database.execute(
            "SELECT * FROM customers WHERE id = ?", 
            invoice_data['customer_id']
        ).fetchone()
        
        if customer['credit_limit'] < invoice_data['amount']:
            raise Exception("Credit limit exceeded")

mcsee

<?php

class Invoice {
    // 1. Identify all public uses of sequential IDs
    // in APIs, URLs, or UI elements   
   
    private string $customerName;
    private array $items;

    public function __construct(