Why Should I Avoid Global Variables in PHP?

Rethinking Global Variables in PHP

While using the global keyword to access variables in other parts of your code may seem convenient, it can lead to unforeseen challenges. Here are some reasons why you should consider avoiding global variables:

Tight Coupling and Dependency:

Global variables establish a tight connection between different parts of your codebase. Any changes to global variable names or existence can cause unexpected breakages throughout the application. To resolve this issue, pass necessary data as function arguments, decoupling components and making them more independent.

Harder to Test and Maintain:

Global variables can make it difficult to test and maintain your code. If a function depends on a global variable, it becomes challenging to test that function in isolation. Injecting dependencies explicitly through function parameters or object properties allows for easier testing and maintainability.

Code Structure and Flow:

Global variables can make your code structure and flow less clear. It can be difficult to understand which parts of your code rely on global variables and their availability. By explicitly passing dependencies, you make the code structure and flow more transparent.

Example Using Dependency Injection:

To demonstrate how to avoid using global variables, consider the following example:

require 'Database.php';
require 'ConfigManager.php';
require 'Log.php';
require 'Foo.php';

// Instantiate database connection
$db = new Database('localhost', 'user', 'pass');

// Load configuration from database (without using global)
$configManager = new ConfigManager;
$config = $configManager->loadConfigurationFromDatabase($db);

// Create logger and pass database connection
$log = new Log($db);

// Create Foo instance and pass configuration
$foo = new Foo($config);

// Execute conversion function with configuration and logger
$foo->conversion('foo', array('bar', 'baz'), $log);

By separating concerns into specific classes and passing data explicitly through dependencies, you create a more flexible, maintainable, and testable codebase.

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