Can parameters of PHP functions be optional? How to declare?

In PHP, use the question mark (?) to declare optional parameters in parameter type annotations, with the default value being null. The optional parameter can be omitted, but a value can also be provided. When an optional parameter is omitted, its default value or null if not provided will be used. This provides flexibility, allowing optional parameters to be used or omitted when needed.

Make the parameters of PHP functions optional

When writing PHP functions, sometimes you need some parameters to be optional , rather than mandatory. Optional parameters allow a function to function correctly when specific parameters are not provided.

Declaring optional parameters

To declare an optional parameter, use a question mark (?) in the parameter type annotation. For example:

function myFunction(int $requiredParam, int $optionalParam = null)
{
    // 函数代码
}

In this example, $requiredParam is a required parameter, $optionalParam is an optional parameter, and its default value is null .

Using optional parameters

When calling a function with optional parameters, you can omit the optional parameters or provide a value:

myFunction(1); //省略可选参数
myFunction(1, 2); //提供可选参数

When optional parameters are omitted, their default values ​​will be used. If no default value is provided, optional parameters will be assigned the value null.

Practical Case

Consider a function that calculates the product of two numbers:

function multiplyNumbers(int $a, int $b)
{
    return $a * $b;
}

If we want to make the second number optional, And to set it to 1 by default, we can use optional parameters:

function multiplyNumbers(int $a, int $b = 1)
{
    return $a * $b;
}

Now, we can call the function like this:

$result1 = multiplyNumbers(2); //第二个数字省略，使用默认值 1
$result2 = multiplyNumbers(2, 5); //提供第二个数字

This approach provides flexibility, allowing the function to adjust as needed Use or omit optional parameters.

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