PHP 7.1–7.3: Nullable, void, iterable and More

PHP 7.1 added nullable types (?string), the void return type, the iterable pseudo-type, class constant visibility, multi-catch (catch (A | B $e)), keyed list() and short array destructuring [$a, $b] = .... PHP 7.2 added the object type and Argon2 password hashing; 7.3 added flexible heredoc syntax, trailing commas in calls, array_key_first/last() and JSON_THROW_ON_ERROR.

<?php
final class UserService
{
    private const CACHE_TTL = 300;          // 7.1: visibility on constants

    public function find(int $id): ?User    // 7.1: nullable
    {
        // ...
    }

    public function logout(): void { /* ... */ }   // 7.1: void
}

try {
    $data = json_decode($body, true, 512, JSON_THROW_ON_ERROR);   // 7.3
} catch (JsonException | InvalidArgumentException $e) {           // 7.1 multi-catch
    return badRequest($e->getMessage());
}

['id' => $id, 'email' => $email] = $row;    // keyed destructuring

Common pitfalls

• Using json_decode() without checking json_last_error() (or the throw flag) and getting null silently.
• Declaring void and still returning a value.
• Relying on iterable and then calling array functions on a Traversable.

Key points

• Nullable and void types (7.1)
• Multi-catch and destructuring
• JSON_THROW_ON_ERROR (7.3)

Further reading: PHP manual: PHP 7.1 new features