How can the type of return value of a PHP function be determined?

Methods to determine the return value type of a PHP function include: 1. Using typehint declaration; 2. Inferring based on function definition; 3. Using gettype() function; 4. Using third-party libraries (such as Psalm and PHPStan).

How to determine the type of PHP function return value

1. Use typehint statement

function greet(string $name): string {
    return "Hello, $name!";
}

Practical case

$name = "John Doe";
$greeting = greet($name);

2. Inference based on function definition

PHP can infer the type based on the return value of the function definition.

function calcSum(int ...$numbers): float {
    return array_sum($numbers);
}

Practical case

$result = calcSum(1, 2, 3);

3. Use gettype() function

This function returns an information string about the variable type.

function checkType($variable) {
    return gettype($variable);
}

Practical case

$variable = 123;
$type = checkType($variable);

4. Using third-party libraries

Some third-party libraries provide additional methods to determine the return value type of a function. For example, [Psalm](https://psalm.dev/) and [PHPStan](https://phpstan.org/) can perform type checking during code analysis.

Practical case (Psalm)

// psalm.xml 配置文件
<?xml version="1.0"?>
<psalm>
    <types>
        <method name="greet" class="App\Greetings">
            <return-type>string</return-type>
        </method>
    </types>
</psalm>

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