Stop Writing WordPress Code That Breaks on Tuesday

I got a call last week about a WooCommerce site where the custom shipping calculator had gone sideways. The client explained that a previous developer built it, but after they left, any attempt to add a new shipping class would either fail silently or, worse, bring down the checkout page. Total mess.

When I finally got into the plugin’s code, I saw the problem immediately. It was a single 2,000-line PHP file full of functions like `calculate_shipping_method_one()`, `calculate_shipping_method_two_new()`, and so on. It was a classic case of a developer who learned PHP exclusively through WordPress hooks and procedural code. This is the exact reason we need to talk about a path to better PHP coding for WordPress developers.

From Plugin Tinkerer to Real Developer

Look, a lot of us got our start with WordPress. It’s an incredible gateway. You solve a small problem for a client with a few hooks in `functions.php`, then you learn to wrap it in a plugin. It feels amazing! You’ve solved a real-world problem. But the danger is staying in that “high school” phase of coding, where everything is a global function and you’re not thinking about structure.

My first instinct with that shipping plugin was to just patch it. Find the right conditional, add another `elseif` statement for the new shipping class, and bill for an hour. And yeah, that would have worked… for now. But I’d just be kicking the can down the road, setting a trap for the next developer. Or, let’s be honest, for myself in six months when another class is added. The real fix had to be architectural.

How WordPress Core Can Teach Better PHP Coding

The problem is, where do you learn these “college-level” concepts? As a community, we often point to frameworks like Symfony or Laravel, but that’s a huge leap. The truth is, WordPress itself should be the next step. This builds on a great concept I saw over at Carl Alexander’s blog about using the WordPress core as a learning gateway. Core has an opportunity to teach by example, but it often falls short by sticking to legacy patterns.

Instead of just patching that broken plugin, I started refactoring it into a class. Here’s the kicker: I didn’t need a massive framework. Just a simple, clean class structure. The first step was defining an interface for what a “shipping method” should be.

<?php

interface ShippingMethodInterface {
    public function get_name();
    public function calculate_cost($weight, $dimensions);
}

// Now, each shipping method is a self-contained class.
class FlatRateShipping implements ShippingMethodInterface {
    public function get_name() {
        return 'Flat Rate';
    }

    public function calculate_cost($weight, $dimensions) {
        // Simple logic for flat rate
        return 15.00;
    }
}

See what this does? It creates a contract. Any new shipping method *must* have a `calculate_cost` method. No more guesswork or similarly named functions. It makes the code predictable and stable. This is the kind of basic Object-Oriented principle—using an `interface`—that would be amazing to see more of in WordPress core components like `WP_Post` or `WP_Widget`.

The Point Isn’t Perfection, It’s Maintainability

This isn’t about being a code purist. It’s about being a professional. Writing code like this means the next developer (or an AI assistant helping with refactoring) can immediately understand the structure and extend it without breaking everything. We can do better than decade-old PHP patterns. It starts with demanding more from ourselves and showing junior devs that there’s a step between hacking `functions.php` and learning a whole new framework.

• Use interfaces to define contracts for your objects.
• Keep your classes small and focused on a single responsibility.
• Use dependency injection instead of relying on global state.

Look, this stuff gets complicated fast. If you’re tired of debugging someone else’s mess and just want your site to work, drop my team a line. We’ve probably seen it before.