How does the parameter passing method of PHP functions interact with external libraries?

There are three ways to pass function parameters in PHP: passing value, passing reference and default value. External library interactions need to consider function signatures, and a common way is to pass values. For example: when using phpmailer to send emails, you need to pass the Message object as a parameter. The default method is to pass by value, which will not affect the object in the external library.

Parameter passing methods of PHP functions and external library interaction

There are three ways to pass parameters of PHP functions: passing value, passing References and default values. For interactions with external libraries, their function signatures need to be considered to determine how parameters are passed.

Passing value

Passing value means assigning the value of the parameter passed when the function is called to the formal parameter. At this point, the formal parameters and actual parameters are independent. For example:

function sum(int $a, int $b) {
    $a += $b;
    return $a;
}

$a = 2;
$b = 3;
$result = sum($a, $b); // $result 为 5，但 $a 依然为 2

Passing by reference

Passing by reference means assigning the reference of the parameter passed when the function is called to the formal parameter. At this time, the formal parameters and actual parameters share the same memory space. For example:

function swap(int &$a, int &$b) {
    $temp = $a;
    $a = $b;
    $b = $temp;
}

$a = 2;
$b = 3;
swap($a, $b); // a=3, b=2

Default value

Default value allows a function to be called without passing certain parameters and assign default values ​​to these parameters. For example:

function greet(string $name = "World") {
    echo "Hello, $name!";
}

greet("John"); // 输出：Hello, John!
greet(); // 输出：Hello, World!

External library interaction practice

The following is a practical case of interaction with an external library:

Scenario: Usephpmailer Send email

External library function signature:

public static function send(Message $message): Message

PHP code:

use PHPMailer\PHPMailer\PHPMailer;

// 实例化 PHPMailer
$mail = new PHPMailer();

// 设置收件人
$mail->addAddress('recipient@example.com');

// 设置邮件正文
$mail->Body = "Hello, this is a test email.";

// 发送邮件并捕获结果
$result = $mail->send();

In this example, the send() function requires a Message object as a parameter, so a Message instance needs to be passed to it. Since the parameter passing method is not specified, the value passing method is used by default, which does not affect the Message object in the external library.

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