What are the type restrictions for PHP function parameters?

PHP function parameter type restrictions can be specified through type hints, which allow the expected type to be specified for parameters. If the passed parameter does not match the type, a TypeError exception will be raised. PHP8 and above support union types, allowing the use of multiple possible types. Static analysis tools can use type hints to detect errors and avoid runtime type mismatches.

Type restrictions of PHP function parameters

PHP supports multiple data types, but the type restrictions of function parameters are very flexible.

Type hints

PHP7 and above support type hints. This feature allows you to specify the expected types for function parameters. If the passed argument does not match the specified type, a TypeError exception will be raised.

Syntax:

function functionName(int $parameter1, string $parameter2): void {
    // ...
}

Optional types

PHP8 and later allow multiple possible types to be specified using union types. If the passed argument matches any of the specified types, no exception will be triggered.

Syntax:

function functionName(int|string $parameter1): void {
    // ...
}

Static Analysis

Some development environments and static analysis tools, such as PhpStorm, can use type hints to detect potential errors. This helps identify and resolve type mismatches before runtime.

Practical case

Suppose we have a function calculateArea to calculate the area of ​​a rectangle:

function calculateArea(int $width, int $height): float {
    return $width * $height;
}

If a non-integer is passed value, the function will trigger a TypeError exception.

try {
    $area = calculateArea(1.5, 2.5);
} catch (TypeError $e) {
    echo $e->getMessage();
}

Output:

Argument 1 passed to calculateArea() must be of the type int, float given

Note:

• Parameter type restrictions are not mandatory. You can still pass parameters to a function that do not match the specified type, but unexpected results may occur.
• Type hints have no runtime overhead. They are only used for compile-time checking.

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