// PHP < 8.3
interface I {
    // We may naively assume that the PHP constant is always a string
    const PHP = 'PHP 8.2';
}

class Foo implements I {
    const PHP = []; // But it may be an array...
}

// PHP 8.3
interface I {
    const string PHP = 'PHP 8.3';
}

class Foo implements I {
    const string PHP = [];
}

// Fatal error: Cannot use array as value for class constant Foo::PHP of type string

// PHP < 8.3
class Foo {
    const PHP = 'PHP 8.2';
}
$searchableConstant = 'PHP';
var_dump(constant(Foo::class . "::{$searchableConstant}"));
// PHP 8.3
class Foo {
    const PHP = 'PHP 8.3';
}
$searchableConstant = 'PHP';
var_dump(Foo::{$searchableConstant});

// PHP < 8.3
use PHPUnit\Framework\TestCase;
final class MyTest extends TestCase
{
    protected $logFile;
    protected function setUp(): void
    {
        $this->logFile = fopen('/tmp/logfile', 'w');
    }
    protected function taerDown(): void
    {
        fclose($this->logFile);
        unlink('/tmp/logfile');
    }
}
// The log file will never be removed, because the
// method name was mistyped (taerDown vs tearDown).
// PHP 8.3
use PHPUnit\Framework\TestCase;
final class MyTest extends TestCase
{
    protected $logFile;
    protected function setUp(): void
    {
        $this->logFile = fopen('/tmp/logfile', 'w');
    }
    #[\Override]
    protected function taerDown(): void
    {
        fclose($this->logFile);
        unlink('/tmp/logfile');
    }
}
// Fatal error: MyTest::taerDown() has #[\Override] attribute,
// but no matching parent method exists

// PHP < 8.3
readonly class Foo {
    public \DateTime $dateTime;
    function __construct(\DateTime $dateTime) {
        $this->dateTime = $dateTime;
    }
    public function __clone()
    {
        $this->dateTime = clone $this->dateTime;
    }
}
$today = new Foo(new \DateTime());
$tomorrow = clone $today;
// Fatal error: Cannot modify readonly property Foo::$dateTime
// PHP 8.3
readonly class Foo {
    public \DateTime $dateTime;
    function __construct(\DateTime $dateTime) {
        $this->dateTime = $dateTime;
    }
    public function __clone()
    {
        $this->dateTime = clone $this->dateTime;
    }
}
$today = new Foo(new \DateTime());
$tomorrow = clone $today;
$tomorrow->dateTime->modify('+1 day');

// PHP < 8.3
function json_validate(string $string): bool {
    json_decode($string);
    return json_last_error() === JSON_ERROR_NONE;
}
var_dump(json_validate('{ "test": { "foo": "bar" } }')); // true
// PHP 8.3
var_dump(json_validate('{ "test": { "foo": "bar" } }')); // true

// PHP < 8.3
php -l index.php
// PHP 8.3
php -l src/**/*.php