PHP Global Variables vs. Parameter Passing: When Should You Use the `global` Keyword?

Global Variables and Functions in PHP

The Utility of the Global Keyword

PHP's global keyword grants functions access to variables defined in the global scope. This allows functions to manipulate global variables as if they were local variables.

Reasons to Prefer One Method Over Another

Security: Using global exposes global variables to the function's local scope, potentially making them vulnerable to modification or unintended manipulation.

Performance: Accessing global variables through the global keyword may cause a performance hit due to increased variable lookups.

Anything Else:

• Testability: Functions using globals are harder to test in isolation as they depend on external variables.
• Maintainability: Code using globals tends to be less readable and maintainable, especially in larger projects.
• 耦合度: Global variables introduce strong coupling between functions and the global scope, making it difficult to reuse or modify code.

Method 1: Passing Variables as Parameters

The preferred method for sharing data between functions is to pass variables as parameters. This maintains encapsulation, simplifies testing, and makes the code more readable and maintainable.

Method 2: Using the Global Keyword

The global keyword should be used only when absolutely necessary, such as when accessing global constants or configuration variables.

When to Use Global Variables

It may be appropriate to use global variables in the following cases:

• Initialization: Setting global constants or configuration settings
• Configuration Management: Reading or updating configuration options that affect multiple parts of the application
• Exceptional Cases: In certain scenarios where passing parameters is impractical or impossible, such as error handling or database connections

Conclusion

While using global variables may seem convenient, it is generally discouraged due to the potential risks associated with security, performance, and code maintainability. It is best practice to avoid using global variables whenever possible and opt for passing variables as parameters instead.

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