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PHP - why global variables are evil

I've recently started working with PHP and while exploring the language, I came across the concept of global variables. However, I've heard from some developers that global variables are considered "evil" or a bad practice. I'm a bit confused about why this is the case.

Can anyone here shed some light on why global variables are often frowned upon in PHP development? What are the potential pitfalls or drawbacks of using global variables? I want to ensure I understand the best practices and avoid any mistakes in my future PHP projects. Any insights or examples would be greatly appreciated. Thank you!

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Hey there! I completely understand your confusion about global variables in PHP. I'll share my personal experience to shed some light on why they are often seen as evil.

In the early days of my PHP journey, I used global variables without giving it much thought. It seemed like a convenient way to access data across multiple functions or scripts without the hassle of passing variables around. However, as my projects grew in complexity, I quickly realized the downsides of this approach.

One major issue with global variables is the potential for unintended side effects. Since they can be accessed and modified from anywhere in the codebase, it becomes challenging to track down changes and ensure data consistency. Bugs tend to be harder to locate and fix, which can result in frustrating debugging sessions.

Furthermore, global variables can lead to tight coupling in your code. When various functions or scripts rely on a global variable, they become tightly connected, making it challenging to reuse or refactor them independently. This can hinder the scalability and flexibility of your codebase, making it harder to adapt and maintain in the long run.

Another drawback of global variables is the lack of clarity and readability in your code. When you rely on global variables, it becomes less obvious where the data is coming from and how it is being used. This can make it harder for other developers (or even yourself in the future) to understand and modify the codebase, reducing overall code quality.

To overcome these issues, I shifted my approach to use local variables and pass them as parameters. By doing so, I ensured that data is encapsulated within specific functions or objects, promoting modularity and reusability. This approach also made my code more self-documenting, as the flow of data became explicit and easier to follow.

While there may be some rare cases where global variables are necessary, I've learned that it's best to avoid them as a general practice. By embracing a more structured approach with local variables and proper parameter passing, you can enhance code maintainability, improve collaboration with other developers, and reduce the likelihood of unexpected bugs.


I completely agree with you that using global variables in PHP can be a slippery slope. In my early days of PHP development, I thought it was convenient to have a single variable accessible throughout my code without having to pass it as a parameter. It seemed like a time-saver and made coding a bit easier.

However, I soon realized the potential issues that global variables can introduce. One major drawback is the lack of encapsulation and potential for variable clashes. Since global variables can be accessed from any part of the codebase, it becomes difficult to keep track of which functions or scripts are modifying or relying on the global variable.

For example, let's say I had a global variable called $count to store the number of times a specific action is performed. If multiple functions or scripts start modifying this variable simultaneously, it can result in unexpected behavior or inaccuracies in the count. This can be a nightmare to debug and maintain.

Moreover, using global variables can make your code less readable and hinder the reusability of your functions. Imagine you come back to a project after a few months and need to make changes. If you have functions that rely on global variables, it becomes much harder to understand the flow of data and dependencies.

Instead, I found that using local variables and passing them as parameters to functions not only promotes encapsulation but also enhances code readability and maintainability. It makes it easier to understand how data flows through the code and minimizes unexpected side effects.

Overall, my personal experience has taught me to be cautious and avoid incorporating global variables in PHP development. It may seem tempting at first, but they often lead to more problems down the line. Embracing local variables and proper parameter passing is a better approach for writing cleaner and more maintainable code.


Oh, global variables in PHP. Where do I even begin? In my experience, using global variables in PHP can quickly turn into a tangled mess that's incredibly difficult to untangle. Trust me, I learned this the hard way.

At first, like you, I thought global variables were a convenient shortcut. I mean, who wants to keep passing variables around all the time, right? But let me tell you, the convenience comes at a cost. It becomes a nightmare to track down and debug issues when multiple functions or scripts start relying on or modifying the same global variable.

I distinctly remember spending countless hours trying to figure out why my code was behaving in such strange ways. Turns out, I had inadvertently made a change to a global variable in one place, only to realize later that it was causing issues in a completely unrelated part of the program. The lack of encapsulation and control over state made my code a complete disaster.

Not only that, but working with global variables also made collaboration with other developers a living nightmare. Imagine trying to work on a codebase where everyone is modifying and relying on global variables. It becomes an unmanageable mess with conflicting changes and an ambiguous understanding of variable states. It's like trying to herd cats!

Thankfully, I've learned my lesson. Nowadays, I steer clear of global variables as much as possible. I've adopted a more structured approach, using local variables and passing them as function parameters. This not only helps in encapsulating data and reducing conflicts but also improves code readability and maintainability.

So, my fellow PHP enthusiast, take it from me – steer clear of global variables if you want to save yourself from endless headaches. Embrace local variables and the joy of passing parameters. Your code will thank you, and your sanity will remain intact. Trust me on this one.

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