The Five Lines of Code Principle: Why Less is More in Programming


In this article, we’ll Learn a simple principle that can help you refactor your code more effectively **“The Five Lines of Code Principle”**. This principle states that **any method should be no longer than five lines of code**. If a method is longer than five lines, it should be broken down into smaller methods that each perform a single responsibility.

In the world of software development, efficiency is key. Whether you’re building an application, a website, or any other piece of software, the goal is always to make it run as smoothly and quickly as possible. One of the most important principles to follow when it comes to writing efficient code is the Five Lines of Code Principle.

### What is the Five Lines of Code Principle?

The Five Lines of Code principle is a programming best practice that emphasizes the importance of keeping functions short and simple. The idea is that a function should be no longer than five lines of code, and ideally even shorter.

This principle is based on the observation that shorter functions are easier to understand, debug, and modify than longer functions. By breaking down a complex task into a series of shorter functions, programmers can create more modular and maintainable code.

### Why five lines of code? What are the key benefits of it?

You might be wondering why five lines of code is a good limit for a method. Why not four, six, or ten? The answer is that five lines of code are not a magic number, but rather a guideline that encourages good coding practices and habits. Here are some of the benefits of following this rule:

 1. **It makes your code more readable:** A short method is easier to understand than a long one, as it has less complexity and noise. It also adheres to the principle of least surprise, which means that it behaves as its name implies and nothing else. A short method also fits better on a screen or a page, which reduces scrolling and eye strain.

 2. **It makes your code more testable:** A short method is easier to test than a long one, as it has fewer inputs and outputs, fewer branches and paths, and fewer dependencies and side effects. It also follows the single responsibility principle, which means that it does one thing and one thing well. A short method also makes your tests more focused and isolated, which improves their quality and reliability.

 3. **It makes your code more maintainable:** A short method is easier to modify than a long one, as it has less coupling and cohesion, less duplication and repetition, and less fragility and rigidity. It also follows the open/closed principle, which means that it is open for extension but closed for modification. A short method also makes your changes more localized and traceable, which reduces the risk of errors and conflicts.

 4. **It makes your code more extensible:** A short method is easier to reuse than a long one, as it has more abstraction and encapsulation, more polymorphism and inheritance, and more composition and delegation. It also follows the interface segregation principle, which means that it provides only what its clients need and nothing more. A short method also makes your code more modular and decoupled, which increases its flexibility and adaptability.

### How to write Five Lines of Code?

The following are some tips to help you write Five Lines of Code:

* **Know your language:** Familiarize yourself with the programming language you’re using, its syntax, built-in functions, and libraries. This knowledge can help you leverage the language’s capabilities and write efficient code.

* **Think outside the box:** To write a program in 5LOC, you need to think creatively and explore different approaches to a problem. The less conventional solution may lead to an optimal code.

* **Use built-in functions and libraries:** Make use of built-in functions, libraries, and frameworks that can help you reduce code complexity and simplify the program’s logic.

* **Keep it simple:** Avoid complex logic, nested loops, or too many conditional statements. Instead, try to break down the problem into smaller, more manageable parts that can be solved with simple code.

* **Optimize for readability:** Although the goal is to write a program in five lines of code, readability should not be sacrificed. Use descriptive variable names and comments to help others understand the code’s purpose and functionality.

### Let’s Understand the “Five Lines of Code Principle” with Ruby example

`calculate_total` is a function that calculates the total price of a shopping cart in an online store.

Step 1: Identify a function that is longer than five lines.

    def calculate_total(cart)
      total = 0
      cart.each do |item|
        price = item[:price]
        price *= (1 - item[:discount]) if item[:discount]
        price *= (1 + item[:tax]) if item[:tax]
        total += price
      end
      total
    end

This function is 10 lines long, which is more than five. So we need to refactor it using the Rule of Five.

Step 2: Find a meaningful chunk of code inside that function that can be extracted into a separate function.

A logical chunk of code that we can extract into a separate function is the one that computes the price of each item, considering the discount and the tax. Since we do this calculation for every item in the cart, it makes sense to wrap it in a function. We can name this functioncalculate_item_price.

Step 3: Give a new function a descriptive name that explains what it does.

    def calculate_item_price(item)
      price = item[:price]
      price *= (1 - item[:discount]) if item[:discount]
      price *= (1 + item[:tax]) if item[:tax]
      price
    end

Step 4: Replace the original chunk of code with the new function.

    def calculate_total(cart)
      total = 0
      cart.each do |item|
        price = calculate_item_price(item)
        total += price
      end
      total
    end

We can make it even shorter by using a built-in method of arrays called, `reduce` which applies a block to each element of an array and accumulates the result.

Step 5: Repeat steps 2–4 until the original function is five lines or less.

    def calculate_total(cart)
      cart.reduce(0) do |total, item|
        total + calculate_item_price(item)
      end
    end

We have successfully refactored it using the Rule of Five. We can also make it more concise by using a one-line block for calculate_item_price.

    def calculate_item_price(item)
      item[:price] * (1 - (item[:discount] || 0)) * (1 + (item[:tax] || 0))
    end
    
    def calculate_total(cart)
      cart.reduce(0) { |total, item| total + calculate_item_price(item) }
    end

Now both functions are one line long, which is very simple and clear. We have completed the example.

### Conclusion

Overall, applying the **Five Lines of Code Principle** is a best practice that can help programmers to create more maintainable, reusable, and efficient code. By breaking down complex tasks into smaller, more manageable functions, programmers can improve code readability, testability, and collaboration, while also identifying and optimizing performance bottlenecks. To implement this principle in your own code, focus on one task per function, use descriptive function names, keep functions short and simple, avoid nested functions, and prioritize readability over brevity. By following these tips, you can create more effective and efficient code that is easier to maintain and understand over time.

By following the steps outlined in this article, you can refactor your code more effectively and keep your codebase healthy.

**Reference:**

* [Five Lines of Codes • Christian Clausen • GOTO 2022 — YouTube](https://www.youtube.com/watch?v=APdaacGmDew)

* If you want to learn more about the Five Lines Of Code Principle and how to apply it in practice, I found the book [Five Lines of Code: How and when to refactor](https://www.amazon.com/Five-Lines-Code-when-refactor/dp/161729831X) by Christian Clausen. It is a great book that teaches you how to refactor your code in a clear, practical, and fun way.

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