haphpiness

void Return Type — Functions That Return Nothing

A function with no return type could mean two very different things: it returns something and nobody bothered to declare it, or it genuinely returns nothing. PHP 7.1 let you say the second one out loud.

// Ambiguous: does this return the user? A bool? Nothing?
function save(User $user) {
    $this->db->persist($user);
}

// Unambiguous, and enforced.
function save(User $user): void {
    $this->db->persist($user);
}

void is stricter than it looks. You may write a bare return; to exit early, but returning an actual value is a compile-time error, not a runtime surprise.

function process(array $items): void {
    if ($items === []) {
        return;              // fine: bare return exits early
    }

    foreach ($items as $item) {
        $this->handle($item);
    }

    return true;             // Fatal error: A void function must not return a value
}

// And calling code cannot pretend otherwise.
$result = process($items);   // $result is null, and static analysis flags the assignment

The payoff is at the call site. : void tells every reader, IDE, and static analyzer that using the return value is meaningless, so PHPStan and Psalm can flag $result = save($user) as a bug rather than shrugging at it. It also documents intent: this function exists for its side effect, and that is the whole point of it.