How to specify access level for PHP functions?

The access level of a PHP function specifies the code access level: Public: Can be accessed by any code. Protected: Accessible by the same class or subclasses. Private: Accessible only by the class in which the function is defined.

Access level specification for PHP functions

In PHP, the access level for a function specifies which code can access the function. You can control the visibility of a function by using access modifiers. The following are the access levels specified in PHP:

1. Public

• The public access level allows any code to access the function, regardless of where it is In the same script or in different scripts.

Example:

public function publicFunction() {
  // 函数代码
}

2. Protected

• The protected access level allows Access this function in the same class or its subclasses.

Example:

protected function protectedFunction() {
  // 函数代码
}

3. Private

• Private access level is only allowed when defined Access the function in the function's class.

Example:

private function privateFunction() {
  // 函数代码
}

Practical Case

Consider the following example where we define in different classes defines functions with different access levels:

class ParentClass {
  public function publicFunction() {
    echo "Public function in parent class";
  }

  protected function protectedFunction() {
    echo "Protected function in parent class";
  }

  private function privateFunction() {
    echo "Private function in parent class";
  }
}

class ChildClass extends ParentClass {
  public function accessFunctions() {
    $this->publicFunction();
    $this->protectedFunction();
    // 错误：对私有函数无访问权限
    $this->privateFunction();
  }
}

// 实例化子类
$child = new ChildClass();

// 调用公共和受保护的函数
$child->publicFunction();
$child->protectedFunction();

In this example, ParentClass defines functions with different access levels, while ChildClass inherits ParentClass. The accessFunctions() method in ChildClass has access to public and protected functions but not to private functions.

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