Understanding Locality of Behaviour in Software Design

Host

Welcome back to the podcast! Today, we’re diving into a fascinating concept in software development called the Locality of Behaviour, or LoB for short. To help us understand this principle, we have Carson Gross, an expert in this field. Carson, welcome!

Expert

Thanks for having me! I'm excited to be here.

Host

Great! So, let's start with the basics—what exactly is the Locality of Behaviour?

Expert

The Locality of Behaviour principle basically states that the behavior of a unit of code should be obvious just by looking at that unit. In other words, when you inspect a piece of code, you should be able to understand what it does without needing to dive into multiple files or sections.

Host

That makes sense! Can you give us an example to illustrate this?

Expert

Sure! Let's compare two ways of handling a button click that makes an AJAX request. In htmx, you might have a simple button like this: `<button hx-get="/clicked">Click Me</button>`. The behavior is clear and directly tied to the button itself.

Host

And what’s the alternative?

Expert

In jQuery, you might write something like this: `$('#d1').on('click', function() { $.ajax({ /* options... */ }); });` Here, the button is separated from its behavior, which is scattered across potentially multiple files. It’s a classic case of ‘spooky action at a distance’—you can’t easily tell what happens when you click that button without knowing the whole codebase.

Host

That sounds like it could lead to a lot of confusion when maintaining the code.

Expert

Exactly! The clearer the relationship between the code and its behavior, the easier it is to maintain, which is why LoB is so important.

Host

Now, I understand that there are trade-offs involved with LoB. Can you explain some of those conflicts?

Expert

Absolutely. One major conflict is with the DRY principle, which stands for 'Don’t Repeat Yourself.' Developers often aim to reduce redundancy in their code. For example, htmx allows you to place attributes on parent elements to avoid repetition in child elements, but this can violate LoB because it obscures the behavior of child elements.

Host

So, it seems like sometimes you have to choose between clarity and avoiding redundancy.

Expert

Exactly! Another principle that can conflict with LoB is Separation of Concerns, which encourages developers to separate different parts of a program, like HTML, CSS, and JavaScript. But when you inline styles or behaviors, you might sacrifice that separation for clarity.

Host

That sounds like a delicate balance to strike. How can developers navigate these trade-offs?

Expert

It’s all about making subjective decisions based on the context. If the behavior is only a few lines away from the code unit, the violation of LoB is less severe than if it’s in a different file. Developers need to be mindful of where they place behaviors in relation to the code they affect.

Host

Thanks, Carson! This has been a really enlightening conversation about the Locality of Behaviour. I appreciate you breaking it down for us.

Expert

My pleasure! It's been great discussing it.

Host

And to our listeners, thanks for tuning in. Until next time, keep questioning and keep learning!