How to write types for formal parameters of methods in PHP

In PHP, the formal parameters of functions and methods can be typed as needed. Writing types for method parameters has the following benefits:

1. Type hints can improve the robustness of the code
   When the parameters of the method are type-hinted, PHP will prevent data of unexpected types Intrusion method to ensure the correctness of the method. For example, if a method needs to receive a string type parameter, PHP will report an error if a numeric type parameter is passed in when the method is called. This prevents unexpected type errors from occurring during code execution.
2. Type hints can make the code more readable
   When the parameters of a method are type hinted, the code writer can easily know what parameters the method requires, and it can also be easy to call the method. Know what parameters to pass. This makes the code clearer and easier to read and maintain.
3. Type hints can improve code scalability
   When the parameters of a method are type hinted, if you need to add new parameters to the method, you only need to add a new parameter type hint. In the code that calls this method, you only need to add the value of the parameter passed in. This makes the code easier to extend and reduces the chance of errors.

So, how to write types for formal parameters of methods in PHP? Here are some methods:

1. Basic data types
   PHP can add type hints for multiple basic data types to formal parameters, including integers (int), floating point numbers (float), Boolean values ​​( bool) and string (string). For example:

function sum(int $a, float $b) {
    return $a + $b;
}
echo sum(1, 2.5); // 输出 3.5

2. Object type
   In PHP, you can also specify the expected object type for the formal parameter. In this way, we can use the methods and properties of the object in the function. For example:

class Person {
    public function getName() {
        return '张三';
    }
}
function sayHello(Person $p) {
    echo 'Hello ' . $p->getName();
}
$p = new Person();
sayHello($p); // 输出 Hello 张三

3. Array type
   In PHP, you can also specify a formal parameter as an array type, and you can further specify the type of array elements. For example:

function foo(array $arr) {
    foreach ($arr as $a) {
        echo $a . ' ';
    }
}
foo([1, 2, 3]); // 输出 1 2 3

4. Nullable type
   After adding a nullable type to a formal parameter, the formal parameter can accept null or the expected type. For example:

function foo(?string $str) {
    if ($str === null) {
        echo 'null';
    } else {
        echo $str;
    }
}
foo(null); // 输出 null
foo('hello'); // 输出 hello

In short, writing type hints for PHP method parameters can make the code more robust, readable, and easy to extend. Therefore, when writing PHP methods, we should make full use of this feature to better build high-quality code.

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