Exploring PHP 8.0’s New Features: Union Types and Named Arguments Explained

Union Return Type Declarations

PHP 8.0 allows a function to declare a union of possible return types, enabling parameters and return values to be either int or float. The example class Stu demonstrates methods add, sub, and mul using these unions.

<?php
class Stu {
    public function add(int|float $a, int|float $b): int {
        return $a + $b;
    }
    public function sub(int|float $a, int|float $b): float|int {
        return $a - $b;
    }
    public function mul(int|float $a, int|float $b, string $c): string {
        return $a + $b;
    }
}
$stu = new Stu();
$rest = $stu->add(10, 20);
var_dump($rest); // int(30)
$rest = $stu->sub(30.25, 20);
var_dump($rest); // float(10.25)
$rest = $stu->mul(30.25, 20, 'extra');
var_dump($rest); // string(5) "50.25"

Named Argument Calls

PHP 8.0 also supports named arguments, allowing callers to specify values by parameter name instead of position. This feature works with union types and variadic parameters, as shown in the following examples.

<?php
class Stu {
    public function add(int $a, int $b): int {
        return $a + $b;
    }
    public function sub(int|float $a, int|float $b, ...$c): float|int {
        // implementation omitted for brevity
    }
}
$stu = new Stu();
$rest = $stu->add(b: 120, a: 100);
var_dump($rest); // int(220)
$rest = $stu->sub(a: 10.3, b: 10);
var_dump($rest); // float(0.3000000000000007)

The article notes that when using named arguments, any subsequent arguments must also be named, otherwise a syntax error occurs.

These new features bring PHP closer to languages like Python, offering greater flexibility in type declarations and argument passing.