使用global關鍵字在PHP函數(shù)中通常被認為是不良實踐。1. 它破壞了函數(shù)的封裝性，導致代碼難以維護、測試和調(diào)試；2. 引發(fā)緊耦合，使函數(shù)依賴全局作用域，降低可重用性；3. 增加測試難度，需額外管理全局狀態(tài)；4. 可能造成不可預期的副作用，因全局變量易被任意修改；5. 降低可讀性，讀者需查找變量定義。替代方案包括：將變量作為參數(shù)傳遞、使用依賴注入、利用常量存儲真正全局且不變的值、重構代碼結構以更好地管理共享狀態(tài)。盡管在遺留系統(tǒng)、簡單腳本或特定框架中偶爾使用global可能合理，但仍應限制其使用并明確記錄原因。總體而言，除非有明確理由并理解權衡，否則應避免使用global。

Yes, using the global keyword inside PHP functions is generally considered bad practice. It breaks the function's encapsulation and makes your code harder to maintain, test, and debug. While it might seem convenient in the short term, especially for small scripts or quick fixes, relying on global can lead to confusing dependencies and unexpected behavior as your application grows.

Why Using global Can Be Problematic

• Tight Coupling: Functions that use global variables become tightly coupled to the global scope. This makes them less reusable and harder to move or refactor.

  

• Harder to Test: Unit testing becomes more complicated because you have to manage global state before each test.

• Unexpected Side Effects: Since global variables can be changed from anywhere, tracking down bugs caused by unintended modifications becomes much harder.

  

• Readability Suffers: When someone reads your function, they need to know what $GLOBALS or global $var; refers to, which isn’t immediately clear unless they look elsewhere in the codebase.

Better Alternatives to Using global

Instead of pulling in global variables with global, consider these alternatives:

• Pass Variables as Parameters
  This keeps your function self-contained and explicit about what it needs.

  function calculateTax($amount, $rate) {
      return $amount * $rate;
  }

• Use Dependency Injection
  Especially useful in object-oriented code. Pass needed values or objects into your class or method rather than relying on global access.

• Utilize Constants (for truly global values)
  If a value is truly meant to be global and unchanging (like a tax rate or API key), define it as a constant instead.

  define('TAX_RATE', 0.15);

• Refactor Your Code Structure
  If you're constantly needing access to global data, it might be a sign your code structure needs improvement—consider moving toward classes or services that manage shared state more cleanly.

When Might It Be Acceptable?

There are rare cases where using global might be acceptable, such as:

• In legacy systems where refactoring would be too costly or risky
• For very simple procedural scripts that won't grow much
• When working with WordPress hooks or certain older frameworks that rely on global variables internally

Even in those cases, it’s best to limit usage and clearly document why global is being used.

In general, avoid global unless you have a very specific reason and understand the trade-offs. Writing cleaner, more predictable functions will save you time and headaches later.

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