How does the parameter passing method of PHP functions handle optional parameters and default parameters?

Parameter passing method: passing by value (basic type) and passing by reference (composite type). Optional parameters: Parameter values ​​are allowed to be specified, but are not required. Default parameters: Allows specifying default values ​​for optional parameters. Practical combat: Demonstrate how to calculate the area of ​​a rectangle using optional and default parameters through an example function.

PHP function parameter passing method

In PHP, function parameters can be passed in two ways:

• Pass by value: Parameters of basic data types (such as integers, floats, and strings) are passed by value, which means that any changes made to the parameters passed will not affects the original variable.
• Pass by reference: Parameters of composite data types (such as arrays and objects) are passed by reference, which means that changes made to the passed parameters also affect the original variables.

Handling optional parameters

Optional parameters allow you to specify parameter values ​​when calling a function, but these parameters are not required. Optional parameters are defined using the following syntax:

function myFunction($requiredParam, $optionalParam = null) {
    // 函数体
}

When calling a function, optional parameters can be omitted, or their values ​​can be specified explicitly. For example:

myFunction('requiredParam'); // 省略可选参数
myFunction('requiredParam', 'optionalParam'); // 指定可选参数值

Handling default parameters

Default parameters allow you to specify default values ​​for optional parameters. Define default parameters using the following syntax:

function myFunction($requiredParam, $optionalParam = 'defaultValue') {
    // 函数体
}

When a function is called, if optional parameters are omitted, the default values ​​will be used. For example:

myFunction('requiredParam'); // 使用默认参数值

Practical case

The following is an example of a function using optional and default parameters:

function calculateArea($length, $width = 1) {
    return $length * $width;
}

$area1 = calculateArea(5); // 省略可选参数，使用默认值 1
$area2 = calculateArea(5, 3); // 指定可选参数值

// 输出结果
echo "面积 1：$area1\n";
echo "面积 2：$area2\n";

Output:

面积 1：5
面积 2：15

The above function calculateArea uses the optional parameter width, and is assigned a default value of 1. When the function is called with the single argument length, the default value width is used. When the function is called with the two parameters length and width, the supplied parameter values ​​will be used.

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