Every developer at some point encounters the challenge of dealing with legacy code. It’s a common story: a codebase built over years, touched by multiple developers, with varying practices, and often lacking documentation. Recently, I found myself in this exact situation while working on an iOS app. The code was riddled with hardcoded values, inconsistent approaches, and little to no explanation of how key parts of the application worked. These issues not only made debugging a nightmare but also complicated the addition of new features.

In this article, I’ll share insights into tackling old issues in legacy code and steps to ensure your codebase evolves in a way that supports future growth rather than becoming a barrier.

Understanding the Challenges of Legacy Code

Hardcoding

Hardcoding embedding fixed values directly into the code might seem convenient during development, but it creates long term problems.

Here, if the tax rate changes or the application needs to support multiple regions with different rates, you’ll need to hunt down and update every occurrence of the hardcoded value. This introduces a high risk of bugs.

let total = price * (1 + 0.15)

Recommended Approach

struct Config {
    static let taxRate = 0.15
}

let total = price * (1 + Config.taxRate)

Using a centralized configuration ensures that updates happen in one place, making the code more maintainable and reducing potential errors.

Inconsistent Practices

Legacy codebases often suffer from inconsistent approaches to solving similar problems.

Wrong Approach:

// Method A
let formatterA = DateFormatter()
formatterA.dateFormat = "yyyy-MM-dd"

// Method B
let formatterB = DateFormatter()
formatterB.dateStyle = .short
formatterB.timeStyle = .none

Using different methods without any standards leads to confusion and wasted time trying to understand which approach to use.

Recommended Approach:

struct DateFormatterUtil {
    static let isoDateFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"
        return formatter
    }()
}

// Usage
let formattedDate = DateFormatterUtil.isoDateFormatter.string(from: date)

By centralizing date formatting logic, you ensure consistency and reusability across the codebase.

Steps to Address Legacy Code Issues

Conduct a Code Audit

Start by reviewing the codebase to identify problematic patterns and redundancies. For example:

Issue Identified: Repeated hardcoded values or unclear function logic.
Solution: Use enums, constants, or descriptive comments to explain their purpose.

// Before
if user.role == "admin" { ... }
if user.role == "editor" { ... }

// After
enum UserRole: String {
    case admin, editor, viewer
}

if user.role == UserRole.admin.rawValue { ... }

Document unclear sections and provide an overview of key functionalities to create a roadmap for refactoring.

Prioritize Incremental Refactoring

Refactor incrementally by improving the code you touch most often. For example, refactor overly complex functions:

Before Refactoring:

func processOrder(order: Order) {
    // Validate
    if order.items.isEmpty {
        print("Invalid order")
    }
    // Calculate total
    let total = order.items.reduce(0) { $0 + $1.price }
    // Process payment
    print("Processing payment of \(total)")
}

After Refactoring:

func validateOrder(order: Order) -> Bool {
    return !order.items.isEmpty
}

func calculateTotal(order: Order) -> Double {
    return order.items.reduce(0) { $0 + $1.price }
}

func processPayment(amount: Double) {
    print("Processing payment of \(amount)")
}

// Usage
if validateOrder(order: order) {
    let total = calculateTotal(order: order)
    processPayment(amount: total)
} else {
    print("Invalid order")
}

This modular approach makes the code more readable, reusable, and testable.

Establish and Enforce Standards

Introduce a consistent coding standard for your team

Wrong Approach:

func calc_disc(price: Double) -> Double { ... }
let usrNm = "John"

Recommended Approach:

func calculateDiscount(price: Double) -> Double { ... }
let userName = "John"

Use linting tools to automate enforcement of these standards, ensuring consistency across the team.

Document Everything

A lack of documentation can leave even simple functions feeling like a black box.

Without Documentation:

func process(data: String) -> String { ... }

With Documentation:

/// Processes input data by sanitizing and normalizing it.
/// - Parameter data: The raw input string.
/// - Returns: A sanitized and normalized string.
func process(data: String) -> String { ... }

Internal documentation is particularly helpful for onboarding new developers and maintaining code over time.

Building a Codebase for the Future

Design for Flexibility

Avoid rigid structures and hardcoding. Use modular design principles to create reusable and adaptable components.

Standardize Practices for Longevity

Adopt a consistent coding style and enforce it through tools and reviews. This ensures that your code remains maintainable and understandable.

Legacy code presents challenges but also offers opportunities for improvement. By addressing hardcoding, introducing consistency, and adopting best practices, you can transform a chaotic codebase into a maintainable, scalable foundation for future growth.