Scope and visibility of function calls in PHP OOP

Scope and visibility of function calls: Scope: Defines the scope (local/global) of variables accessible to the function. Visibility: Define the scope of the function that can be accessed by other functions (public/protected/private). Scope takes effect when a function is called and determines the variables that are accessible. Practical case: Take the User class as an example to demonstrate the visibility restrictions of properties and methods.

Scope and visibility of function calls in PHP OOP

Scope

The scope of a function defines the scope of variables accessible to the function. There are two types of scopes in PHP:

• Local scope: Variables defined inside a function are only visible inside that function.
• Global scope: Variables defined outside the function are accessible throughout the script.

Visibility

The visibility of a function defines the scope within which the function can be accessed by other functions. There are three visibility levels in PHP:

• public: Functions can be accessed from anywhere.
• protected: Functions can only be accessed in subclasses of this class.
• private: Functions can only be accessed within this class.

Scope of function calls

When a function is called, the role of the scope is to determine which variables can be accessed. A variable can only access variables within its scope.

The following example shows how scope affects variable access:

<?php
$global_variable = "全球变量";

function myFunction() {
    $local_variable = "局部变量";
    echo "局部变量：$local_variable<br>";
    echo "全局变量：$global_variable<br>";
}

myFunction();
?>

Output:

局部变量：局部变量
全局变量：全球变量

Practical case

Consider a class used to handle user information:

<?php
class User {
    public $name;
    protected $email;
    private $password;

    public function __construct($name, $email, $password) {
        $this->name = $name;
        $this->email = $email;
        $this->password = $password;
    }

    public function getName() {
        return $this->name;
    }

    protected function getEmail() {
        return $this->email;
    }

    private function getPassword() {
        return $this->password;
    }
}

$user = new User("约翰·史密斯", "john.smith@example.com", "12345");

echo $user->getName(); // 约翰·史密斯
echo $user->getEmail(); // 错误：无法访问受保护属性
echo $user->getPassword(); // 错误：无法访问私有属性
?>

In this example:

• $name is a public property that can be used in Access anywhere.
• $email is a protected property and can only be accessed within subclasses of class とその.
• $password is a private property and can only be accessed within the class.
• getName() is a public method that can be called anywhere.
• getEmail() is a protected method and can only be called in subclasses of class とその.
• getPassword() is a private method that can only be called in the class.

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