Level-Up as a Developer by Working with Legacy Codebases

Here's a list of topics and resources to use the next time you have a little down-time. Applying these skills will help you write more maintainable code. Over time you will also gain a reputation for being the kind of developer people turn to when they have a thorny problem to solve.

Functional Programming Basics

Functional Programming is a vast subject, but you can start to see benefits from the understanding of a single concept: Pure Functions. Let's start with a simple definition 👇

Pure vs Impure Functions in Functional Programming – What's the Difference?

Pure functions and impure functions are two programming terms you will often see in functional programming. One core difference between these two types of functions is whether or not they have side effects. In this article, you will learn what side effects are and we'll discuss the differences between pure

freecodecamp.org

This next video👇explains how to use it in your software.

Note: He refers to pure-functions as "calculations" and side-effects as "actions", so keep that in mind.

You will only learn by doing, so if you'd like to practice:

• Go through your current code-base
• Look for a Function where the side-effects and business-logic are mixed together
  • ideally you already understand the details of the function really well
• Separate out the Business Logic into a Pure-Function with just the "Calculations", and keep it separate from your side-effects.
  • Ensure your application still works.

If you would like an example, here's code for an example ShoppingCart Class where you can add items and a discount is calculated before checkout:

• Business Logic mixed with Side-Effects
• Business Logic separated into a Pure Function

Why would you want to do this though.

• Most bugs tend to be in the Business Logic
• If a Function or a Class logs to a DB or sends an email every time it's run, it becomes harder to test properly.
• If you can extract a Calculation into a Pure Function, it becomes easier to run.
• The easier it becomes to run, the easier it is to fix bugs.
• You can even write unit-tests for your Pure-Functions and run them automatically on every change, making it easier to catch regressions.

Next Steps

There's a few other skills I think make it easier to work with old code, I'm going to add those in shortly:

• TDD, for better-quality pure-functions
• C4 Architecture Diagrams, for standardized documentation
• Sequence Flow Diagrams in Mermaid, to get quicker feedback on code
• Trunk Based Development, to reduce operational overhead for small teams
• CodeScene, to manage the health of a codebase and pay-down tech-debt
• Approval Testing, when the original devs on a project aren't available

Leave me a comment or DM me on Twitter if you have any specific requests or questions.