diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 91fba22..e68daf1 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        php: ['7.2', '7.3', '7.4', '8.0']
+        php: ['8.0', '8.1', '8.2', '8.3']
     name: PHP ${{ matrix.php }} Test on ${{ matrix.os }}
     steps:
       - name: Checkout
@@ -18,7 +18,6 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
-          extensions: curl
           coverage: none
 
       - name: Install dependencies
diff --git a/composer.json b/composer.json
index a9b2ece..1ee0a4e 100644
--- a/composer.json
+++ b/composer.json
@@ -5,14 +5,14 @@
     "keywords": ["command-bus", "command", "service-bus"],
     "license": "MIT",
     "require": {
-        "php": "^7.2 || ^8.0",
+        "php": "^8.0",
         "psr/container": "^1.0 || ^2.0",
         "psr/log": "^1.1 || ^2.0",
         "php-amqplib/php-amqplib": "^2.12 || ^3.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^8.5|^9.0",
-        "phpstan/phpstan": "^0.12.14"
+        "phpstan/phpstan": "^1.10"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Builder.php b/src/Builder.php
index c3d2e42..2e85812 100644
--- a/src/Builder.php
+++ b/src/Builder.php
@@ -12,17 +12,17 @@ final class Builder
     /**
      * @var array<string, callable>
      */
-    private $handlers = [];
+    private array $handlers = [];
 
     /**
      * @var array<string, Middleware>
      */
-    private $middleware = [];
+    private array $middleware = [];
 
     /**
      * @var array<string, Extension>
      */
-    private $extensions = [];
+    private array $extensions = [];
 
     /**
      * @param string   $command
diff --git a/src/Context.php b/src/Context.php
index 944aa8e..d1f429f 100644
--- a/src/Context.php
+++ b/src/Context.php
@@ -4,42 +4,25 @@
 
 namespace Onliner\CommandBus;
 
-use Onliner\CommandBus\Message\MessageIterator;
+use Onliner\CommandBus\Message\DeferredIterator;
 
 final class Context
 {
     /**
-     * @var Dispatcher
+     * @param Dispatcher           $dispatcher
+     * @param DeferredIterator     $deferred
+     * @param array<string, mixed> $options
      */
-    private $dispatcher;
-
-    /**
-     * @var MessageIterator
-     */
-    private $deferred;
-
-    /**
-     * @var array<mixed>
-     */
-    private $options;
-
-    /**
-     * @internal
-     *
-     * @param Dispatcher             $dispatcher
-     * @param MessageIterator<array> $deferred
-     * @param array<mixed>           $options
-     */
-    public function __construct(Dispatcher $dispatcher, MessageIterator $deferred, array $options = [])
-    {
-        $this->dispatcher = $dispatcher;
-        $this->deferred = $deferred;
-        $this->options = $options;
+    public function __construct(
+        private Dispatcher $dispatcher,
+        private DeferredIterator $deferred,
+        private array $options = []
+    ) {
     }
 
     /**
-     * @param object       $message
-     * @param array<mixed> $options
+     * @param object               $message
+     * @param array<string, mixed> $options
      *
      * @return void
      */
@@ -49,8 +32,8 @@ public function dispatch(object $message, array $options = []): void
     }
 
     /**
-     * @param object       $message
-     * @param array<mixed> $options
+     * @param object               $message
+     * @param array<string, mixed> $options
      *
      * @return self
      */
@@ -62,7 +45,7 @@ public function defer(object $message, array $options = []): self
     }
 
     /**
-     * @return array<mixed>
+     * @return array<string, mixed>
      */
     public function all(): array
     {
@@ -85,7 +68,7 @@ public function has(string $option): bool
      *
      * @return mixed
      */
-    public function get(string $option, $default = null)
+    public function get(string $option, mixed $default = null): mixed
     {
         return $this->options[$option] ?? $default;
     }
@@ -96,7 +79,7 @@ public function get(string $option, $default = null)
      *
      * @return self
      */
-    public function set(string $option, $value): self
+    public function set(string $option, mixed $value): self
     {
         $this->options[$option] = $value;
 
diff --git a/src/Dispatcher.php b/src/Dispatcher.php
index c494d32..38c05a3 100644
--- a/src/Dispatcher.php
+++ b/src/Dispatcher.php
@@ -4,41 +4,33 @@
 
 namespace Onliner\CommandBus;
 
-use Onliner\CommandBus\Message\MessageIterator;
+use Onliner\CommandBus\Message\DeferredIterator;
 
 final class Dispatcher
 {
-    /**
-     * @var Resolver
-     */
-    private $resolver;
-
     /**
      * @param Resolver $resolver
      */
-    public function __construct(Resolver $resolver)
+    public function __construct(private Resolver $resolver)
     {
-        $this->resolver = $resolver;
     }
 
     /**
-     * @param object       $message
-     * @param array<mixed> $options
+     * @param object               $message
+     * @param array<string, mixed> $options
      *
      * @return void
      */
     public function dispatch(object $message, array $options = []): void
     {
         $handler = $this->resolver->resolve($message);
-        $deferred = new MessageIterator();
-        $context = new Context($this, $deferred, $options);
+        $iterator = new DeferredIterator();
+        $context = new Context($this, $iterator, $options);
 
         $handler($message, $context);
 
-        foreach ($deferred as $item) {
-            [$deferredMessage, $deferredOptions] = $item;
-
-            $this->dispatch($deferredMessage, $deferredOptions);
+        foreach ($iterator as $deferred) {
+            $this->dispatch($deferred->message, $deferred->options);
         }
     }
 }
diff --git a/src/Exception/InvalidHandlerException.php b/src/Exception/InvalidHandlerException.php
new file mode 100644
index 0000000..661fa29
--- /dev/null
+++ b/src/Exception/InvalidHandlerException.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Onliner\CommandBus\Exception;
+
+final class InvalidHandlerException extends CommandBusException
+{
+    public function __construct(string $class)
+    {
+        parent::__construct(sprintf('Handler for command "%s" must be callable.', $class));
+    }
+}
diff --git a/src/Exception/InvalidMessageException.php b/src/Exception/InvalidMessageException.php
new file mode 100644
index 0000000..091c620
--- /dev/null
+++ b/src/Exception/InvalidMessageException.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Onliner\CommandBus\Exception;
+
+final class InvalidMessageException extends CommandBusException
+{
+    public function __construct(string $class)
+    {
+        parent::__construct(sprintf('Invalid message for class "%s".', $class));
+    }
+}
diff --git a/src/Exception/UnknownHandlerException.php b/src/Exception/UnknownHandlerException.php
index de0b7d1..212edff 100644
--- a/src/Exception/UnknownHandlerException.php
+++ b/src/Exception/UnknownHandlerException.php
@@ -6,8 +6,8 @@
 
 final class UnknownHandlerException extends CommandBusException
 {
-    public static function forCommand(object $command): self
+    public function __construct(string $class)
     {
-        return new self(sprintf('Handler for command "%s" not found.', get_class($command)));
+        parent::__construct(sprintf('Handler for command "%s" not found.', $class));
     }
 }
diff --git a/src/Message/Deferred.php b/src/Message/Deferred.php
new file mode 100644
index 0000000..66c5cb7
--- /dev/null
+++ b/src/Message/Deferred.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Onliner\CommandBus\Message;
+
+class Deferred
+{
+    /**
+     * @param object               $message
+     * @param array<string, mixed> $options
+     */
+    public function __construct(
+        public object $message,
+        public array $options,
+    ) {
+    }
+}
diff --git a/src/Message/MessageIterator.php b/src/Message/DeferredIterator.php
similarity index 50%
rename from src/Message/MessageIterator.php
rename to src/Message/DeferredIterator.php
index 1fa67da..cde7371 100644
--- a/src/Message/MessageIterator.php
+++ b/src/Message/DeferredIterator.php
@@ -8,30 +8,30 @@
 use IteratorAggregate;
 
 /**
- * @implements IteratorAggregate<array>
+ * @implements IteratorAggregate<Deferred>
  */
-class MessageIterator implements IteratorAggregate
+class DeferredIterator implements IteratorAggregate
 {
     /**
-     * @var array<array>
+     * @var array<Deferred>
      */
-    private $messages = [];
+    private array $messages = [];
 
     /**
-     * @param object       $message
-     * @param array<mixed> $options
+     * @param object               $message
+     * @param array<string, mixed> $options
      *
-     * @return self<array>
+     * @return self
      */
     public function append(object $message, array $options): self
     {
-        $this->messages[] = [$message, $options];
+        $this->messages[] = new Deferred($message, $options);
 
         return $this;
     }
 
     /**
-     * @return Generator<array>
+     * @return Generator<Deferred>
      */
     public function getIterator(): Generator
     {
diff --git a/src/Middleware/LoggerMiddleware.php b/src/Middleware/LoggerMiddleware.php
index 7e85ee7..e4c4fec 100644
--- a/src/Middleware/LoggerMiddleware.php
+++ b/src/Middleware/LoggerMiddleware.php
@@ -12,24 +12,12 @@
 
 final class LoggerMiddleware implements Middleware
 {
-    /**
-     * @var LoggerInterface
-     */
-    private $logger;
-
-    /**
-     * @var string
-     */
-    private $level;
-
     /**
      * @param LoggerInterface $logger
      * @param string          $level
      */
-    public function __construct(LoggerInterface $logger, string $level = LogLevel::ERROR)
+    public function __construct(private LoggerInterface $logger, private string $level = LogLevel::ERROR)
     {
-        $this->logger = $logger;
-        $this->level  = $level;
     }
 
     /**
diff --git a/src/Remote/AMQP/AMQPConsumer.php b/src/Remote/AMQP/AMQPConsumer.php
index 37e5336..870b8a5 100644
--- a/src/Remote/AMQP/AMQPConsumer.php
+++ b/src/Remote/AMQP/AMQPConsumer.php
@@ -11,6 +11,7 @@
 use PhpAmqpLib\Exception\AMQPConnectionClosedException;
 use PhpAmqpLib\Exception\AMQPIOException;
 use PhpAmqpLib\Message\AMQPMessage;
+use PhpAmqpLib\Wire\AMQPAbstractCollection;
 use Psr\Log\LoggerInterface;
 use Psr\Log\NullLogger;
 use Throwable;
@@ -28,41 +29,25 @@ final class AMQPConsumer implements Consumer
         DEFAULT_INTERVAL = 1000000
     ;
 
-    /**
-     * @var Connector
-     */
-    private $connector;
-
-    /**
-     * @var Exchange
-     */
-    private $exchange;
+    private LoggerInterface $logger;
+    private bool $running = false;
 
     /**
-     * @var LoggerInterface
+     * @var Queue[]
      */
-    private $logger;
-
-    /**
-     * @var array<Queue>
-     */
-    private $queues = [];
-
-    /**
-     * @var bool
-     */
-    private $running = false;
+    private array $queues = [];
 
     /**
      * @param Connector            $connector
      * @param Exchange             $exchange
      * @param LoggerInterface|null $logger
      */
-    public function __construct(Connector $connector, Exchange $exchange, LoggerInterface $logger = null)
-    {
-        $this->connector = $connector;
-        $this->exchange  = $exchange;
-        $this->logger    = $logger ?? new NullLogger();
+    public function __construct(
+        private Connector $connector,
+        private Exchange $exchange,
+        LoggerInterface $logger = null
+    ) {
+        $this->logger = $logger ?? new NullLogger();
     }
 
     /**
@@ -193,8 +178,15 @@ private function connect(array $options): AMQPChannel
      */
     private function handle(AMQPMessage $message, Dispatcher $dispatcher): void
     {
-        $headers = $message->get('application_headers')->getNativeData();
-        $headers = array_merge($headers, [
+        $headers = $message->get('application_headers');
+
+        if (!$headers instanceof AMQPAbstractCollection) {
+            $this->logger->warning('Message headers not found.');
+
+            return;
+        }
+
+        $headers = array_replace($headers->getNativeData(), [
             Exchange::HEADER_EXCHANGE     => $message->getExchange(),
             Exchange::HEADER_ROUTING_KEY  => $message->getRoutingKey(),
             Exchange::HEADER_CONSUMER_TAG => $message->getConsumerTag(),
@@ -208,8 +200,9 @@ private function handle(AMQPMessage $message, Dispatcher $dispatcher): void
             return;
         }
 
-        $type = $headers[Exchange::HEADER_MESSAGE_TYPE];
+        /** @var class-string $class */
+        $class = $headers[Exchange::HEADER_MESSAGE_TYPE];
 
-        $dispatcher->dispatch(new Envelope($type, $message->getBody(), $headers));
+        $dispatcher->dispatch(new Envelope($class, $message->getBody(), $headers));
     }
 }
diff --git a/src/Remote/AMQP/AMQPFlags.php b/src/Remote/AMQP/AMQPFlags.php
index 0f744bb..615c588 100644
--- a/src/Remote/AMQP/AMQPFlags.php
+++ b/src/Remote/AMQP/AMQPFlags.php
@@ -28,17 +28,11 @@ class AMQPFlags
         'no_ack'    => self::NO_ACK,    // Used only for consume
     ];
 
-    /**
-     * @var int
-     */
-    private $value;
-
     /**
      * @param int $value
      */
-    public function __construct(int $value)
+    public function __construct(private int $value)
     {
-        $this->value = $value;
     }
 
     /**
diff --git a/src/Remote/AMQP/AMQPTransport.php b/src/Remote/AMQP/AMQPTransport.php
index b2fde78..a6ef838 100644
--- a/src/Remote/AMQP/AMQPTransport.php
+++ b/src/Remote/AMQP/AMQPTransport.php
@@ -11,7 +11,6 @@
 use PhpAmqpLib\Message\AMQPMessage;
 use PhpAmqpLib\Wire\AMQPTable;
 use Psr\Log\LoggerInterface;
-use Psr\Log\NullLogger;
 
 final class AMQPTransport implements Transport
 {
@@ -19,42 +18,18 @@ final class AMQPTransport implements Transport
         'delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT,
     ];
 
-    /**
-     * @var Connector
-     */
-    private $connector;
-
-    /**
-     * @var Exchange
-     */
-    private $exchange;
-
-    /**
-     * @var Router
-     */
-    private $router;
-
-    /**
-     * @var LoggerInterface
-     */
-    private $logger;
-
     /**
      * @param Connector            $connector
      * @param Exchange             $exchange
-     * @param Router|null          $router
+     * @param Router               $router
      * @param LoggerInterface|null $logger
      */
     public function __construct(
-        Connector $connector,
-        Exchange $exchange,
-        Router $router = null,
-        LoggerInterface $logger = null
+        private Connector $connector,
+        private Exchange $exchange,
+        private Router $router,
+        private ?LoggerInterface $logger = null
     ) {
-        $this->connector = $connector;
-        $this->exchange  = $exchange;
-        $this->router    = $router ?? new SimpleRouter();
-        $this->logger    = $logger ?? new NullLogger();
     }
 
     /**
@@ -65,9 +40,13 @@ public function __construct(
      */
     public static function create(string $dsn, array $options = []): self
     {
-        $resolver = new SimpleRouter($options['routes'] ?? []);
+        if (!is_array($routes = $options['routes'] ?? false)) {
+            $routes = [];
+        }
+
+        $router = new SimpleRouter(array_filter($routes, 'is_string'));
 
-        return new self(Connector::create($dsn), Exchange::create($options), $resolver);
+        return new self(Connector::create($dsn), Exchange::create($options), $router);
     }
 
     /**
@@ -76,7 +55,7 @@ public static function create(string $dsn, array $options = []): self
     public function send(Envelope $envelope): void
     {
         $headers = $envelope->headers + [
-            Exchange::HEADER_MESSAGE_TYPE => $envelope->type,
+            Exchange::HEADER_MESSAGE_TYPE => $envelope->class,
         ];
 
         $message = new AMQPMessage($envelope->payload, self::MESSAGE_PROPERTIES);
@@ -90,8 +69,6 @@ public function send(Envelope $envelope): void
             $message,
             $route->exchange(),
             $route->name(),
-            false,
-            false
         );
     }
 
diff --git a/src/Remote/AMQP/Connector.php b/src/Remote/AMQP/Connector.php
index 544599b..39fe260 100644
--- a/src/Remote/AMQP/Connector.php
+++ b/src/Remote/AMQP/Connector.php
@@ -12,34 +12,15 @@
 
 class Connector
 {
-    /**
-     * @var array<array<mixed>>
-     */
-    private $hosts;
-
-    /**
-     * @var array<string, mixed>
-     */
-    private $options;
-
-    /**
-     * @var AMQPChannel|null
-     */
-    private $channel;
-
-    /**
-     * @var PCNTLHeartbeatSender|null
-     */
-    private $heartbeats;
+    private ?AMQPChannel $channel = null;
+    private ?PCNTLHeartbeatSender $heartbeats = null;
 
     /**
-     * @param array<array<mixed>> $hosts
-     * @param array<string, mixed> $options
+     * @param array<array<mixed>>      $hosts
+     * @param array<string|int, mixed> $options
      */
-    public function __construct(array $hosts, array $options)
+    public function __construct(private array $hosts, private array $options)
     {
-        $this->hosts = $hosts;
-        $this->options = $options;
     }
 
     /**
@@ -100,12 +81,7 @@ public function connect(): AMQPChannel
 
     public function __destruct()
     {
-        if ($this->heartbeats !== null) {
-            $this->heartbeats->unregister();
-        }
-
-        if ($this->channel !== null) {
-            $this->channel->close();
-        }
+        $this->heartbeats?->unregister();
+        $this->channel?->close();
     }
 }
diff --git a/src/Remote/AMQP/Exchange.php b/src/Remote/AMQP/Exchange.php
index 8cc5d72..6eafc80 100644
--- a/src/Remote/AMQP/Exchange.php
+++ b/src/Remote/AMQP/Exchange.php
@@ -4,6 +4,7 @@
 
 namespace Onliner\CommandBus\Remote\AMQP;
 
+use InvalidArgumentException;
 use PhpAmqpLib\Channel\AMQPChannel;
 use PhpAmqpLib\Wire\AMQPTable;
 
@@ -26,25 +27,7 @@ final class Exchange
         HEADER_MESSAGE_TYPE = 'x-message-type'
     ;
 
-    /**
-     * @var string
-     */
-    private $name;
-
-    /**
-     * @var string
-     */
-    private $type;
-
-    /**
-     * @var AMQPFlags
-     */
-    private $flags;
-
-    /**
-     * @var array<string, string>
-     */
-    private $args;
+    private AMQPFlags $flags;
 
     /**
      * @param string                 $name
@@ -53,15 +36,12 @@ final class Exchange
      * @param array<string, string>  $args
      */
     public function __construct(
-        string $name,
-        string $type = self::TYPE_TOPIC,
+        private string $name,
+        private string $type = self::TYPE_TOPIC,
         AMQPFlags $flags = null,
-        array $args = []
+        private array $args = []
     ) {
-        $this->name  = $name;
-        $this->type  = $type;
         $this->flags = $flags ?? AMQPFlags::default();
-        $this->args  = $args;
     }
 
     /**
@@ -72,15 +52,27 @@ public function __construct(
     public static function create(array $options): self
     {
         $type  = $options['type'] ?? self::TYPE_TOPIC;
-        $name  = $options['exchange'] ?? sprintf('amqp.%s', $type);
-        $flags = AMQPFlags::compute($options);
-        $args  = $options['args'] ?? [];
+
+        if (!is_string($type)) {
+            throw new InvalidArgumentException('Exchange type must be a string');
+        }
+
+        $name = $options['exchange'] ?? sprintf('amqp.%s', $type);
+        $args = $options['args'] ?? [];
+
+        if (!is_string($name)) {
+            throw new InvalidArgumentException('Exchange name must be a string');
+        }
+
+        if (!is_array($args)) {
+            throw new InvalidArgumentException('Exchange arguments must be an array');
+        }
 
         if ($type === self::TYPE_DELAYED && !isset($args['x-delayed-type'])) {
             $args['x-delayed-type'] = self::TYPE_TOPIC;
         }
 
-        return new self($name, $type, $flags, $args);
+        return new self($name, $type, AMQPFlags::compute($options), $args);
     }
 
     /**
diff --git a/src/Remote/AMQP/Headers.php b/src/Remote/AMQP/Headers.php
new file mode 100644
index 0000000..e5d185f
--- /dev/null
+++ b/src/Remote/AMQP/Headers.php
@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Onliner\CommandBus\Remote\AMQP;
+
+class Headers
+{
+    public const DELAY = 'x-delay';
+    public const PRIORITY = 'x-priority';
+}
diff --git a/src/Remote/AMQP/Queue.php b/src/Remote/AMQP/Queue.php
index a64a27b..4c5d2c2 100644
--- a/src/Remote/AMQP/Queue.php
+++ b/src/Remote/AMQP/Queue.php
@@ -4,6 +4,7 @@
 
 namespace Onliner\CommandBus\Remote\AMQP;
 
+use InvalidArgumentException;
 use PhpAmqpLib\Channel\AMQPChannel;
 use PhpAmqpLib\Wire\AMQPTable;
 
@@ -16,25 +17,8 @@ final class Queue
         DEAD_LETTER  = 'x-dead-letter-exchange'
     ;
 
-    /**
-     * @var string
-     */
-    private $name;
-
-    /**
-     * @var string
-     */
-    private $pattern;
-
-    /**
-     * @var AMQPFlags
-     */
-    private $flags;
-
-    /**
-     * @var array<string, string>
-     */
-    private $args;
+    private string $pattern;
+    private AMQPFlags $flags;
 
     /**
      * @param string                $name
@@ -42,12 +26,14 @@ final class Queue
      * @param AMQPFlags|null        $flags
      * @param array<string, string> $args
      */
-    public function __construct(string $name, string $pattern = null, AMQPFlags $flags = null, array $args = [])
-    {
-        $this->name    = $name;
+    public function __construct(
+        private string $name,
+        string $pattern = null,
+        AMQPFlags $flags = null,
+        private array $args = []
+    ) {
         $this->pattern = $pattern ?? $name;
         $this->flags   = $flags ?? AMQPFlags::default();
-        $this->args    = $args;
     }
 
     /**
@@ -58,9 +44,22 @@ public function __construct(string $name, string $pattern = null, AMQPFlags $fla
     public static function create(array $options): self
     {
         $pattern = $options['pattern'] ?? '#';
-        $name    = $options['queue'] ?? $pattern;
+        $name = $options['queue'] ?? $pattern;
+        $args = $options['args'] ?? [];
+
+        if (!is_string($name)) {
+            throw new InvalidArgumentException('Queue name must be a string');
+        }
+
+        if ($pattern !== null && !is_string($pattern)) {
+            throw new InvalidArgumentException('Queue pattern must be a string or null');
+        }
+
+        if (!is_array($args)) {
+            throw new InvalidArgumentException('Queue arguments must be an array');
+        }
 
-        return new self($name, $pattern, AMQPFlags::compute($options), $options['args'] ?? []);
+        return new self($name, $pattern, AMQPFlags::compute($options), $args);
     }
 
     /**
diff --git a/src/Remote/AMQP/Route.php b/src/Remote/AMQP/Route.php
index a4938af..11aabd0 100644
--- a/src/Remote/AMQP/Route.php
+++ b/src/Remote/AMQP/Route.php
@@ -6,24 +6,12 @@
 
 final class Route
 {
-    /**
-     * @var string
-     */
-    private $exchange;
-
-    /**
-     * @var string
-     */
-    private $name;
-
     /**
      * @param string $exchange
      * @param string $name
      */
-    public function __construct(string $exchange, string $name)
+    public function __construct(private string $exchange, private string $name)
     {
-        $this->exchange = $exchange;
-        $this->name     = $name;
     }
 
     /**
diff --git a/src/Remote/AMQP/Router/SimpleRouter.php b/src/Remote/AMQP/Router/SimpleRouter.php
index 730665d..5719f16 100644
--- a/src/Remote/AMQP/Router/SimpleRouter.php
+++ b/src/Remote/AMQP/Router/SimpleRouter.php
@@ -5,23 +5,17 @@
 namespace Onliner\CommandBus\Remote\AMQP\Router;
 
 use Onliner\CommandBus\Remote\AMQP\Exchange;
-use Onliner\CommandBus\Remote\AMQP\Router;
 use Onliner\CommandBus\Remote\AMQP\Route;
+use Onliner\CommandBus\Remote\AMQP\Router;
 use Onliner\CommandBus\Remote\Envelope;
 
 final class SimpleRouter implements Router
 {
     /**
-     * @var array<string,mixed>
-     */
-    private $routes;
-
-    /**
-     * @param array<string,mixed> $routes
+     * @param array<string, string> $routes
      */
-    public function __construct(array $routes = [])
+    public function __construct(private array $routes = [])
     {
-        $this->routes = $routes;
     }
 
     /**
@@ -29,8 +23,8 @@ public function __construct(array $routes = [])
      */
     public function match(Envelope $envelope, Exchange $exchange): Route
     {
-        $target = $this->exchange($envelope->type, $exchange->name());
-        $name = strtolower(str_replace('\\', '.', $envelope->type));
+        $target = $this->exchange($envelope->class, $exchange->name());
+        $name = strtolower(str_replace('\\', '.', $envelope->class));
 
         return new Route($target, $name);
     }
diff --git a/src/Remote/Envelope.php b/src/Remote/Envelope.php
index 485237f..136cc01 100644
--- a/src/Remote/Envelope.php
+++ b/src/Remote/Envelope.php
@@ -7,29 +7,11 @@
 final class Envelope
 {
     /**
-     * @var string
-     */
-    public $type;
-
-    /**
-     * @var string
-     */
-    public $payload;
-
-    /**
-     * @var array<mixed>
-     */
-    public $headers;
-
-    /**
-     * @param string       $type
+     * @param class-string $class
      * @param string       $payload
      * @param array<mixed> $headers
      */
-    public function __construct(string $type, string $payload, array $headers = [])
+    public function __construct(public string $class, public string $payload, public array $headers = [])
     {
-        $this->type    = $type;
-        $this->payload = $payload;
-        $this->headers = $headers;
     }
 }
diff --git a/src/Remote/Gateway.php b/src/Remote/Gateway.php
index ff4507b..d933ab4 100644
--- a/src/Remote/Gateway.php
+++ b/src/Remote/Gateway.php
@@ -10,24 +10,12 @@ final class Gateway
 {
     public const OPTION_LOCAL = 'local';
 
-    /**
-     * @var Transport
-     */
-    private $transport;
-
-    /**
-     * @var Serializer
-     */
-    private $serializer;
-
     /**
      * @param Transport  $transport
      * @param Serializer $serializer
      */
-    public function __construct(Transport $transport, Serializer $serializer)
+    public function __construct(private Transport $transport, private Serializer $serializer)
     {
-        $this->transport  = $transport;
-        $this->serializer = $serializer;
     }
 
     /**
diff --git a/src/Remote/RemoteExtension.php b/src/Remote/RemoteExtension.php
index f138804..8adcddd 100644
--- a/src/Remote/RemoteExtension.php
+++ b/src/Remote/RemoteExtension.php
@@ -9,20 +9,13 @@
 
 final class RemoteExtension implements Extension
 {
-    /**
-     * @var Transport
-     */
-    private $transport;
-
-    /**
-     * @var Serializer
-     */
-    private $serializer;
+    private Transport $transport;
+    private Serializer $serializer;
 
     /**
      * @var array<string>
      */
-    private $local = [
+    private array $local = [
         Envelope::class,
     ];
 
diff --git a/src/Remote/RemoteMiddleware.php b/src/Remote/RemoteMiddleware.php
index 17a2b03..b274812 100644
--- a/src/Remote/RemoteMiddleware.php
+++ b/src/Remote/RemoteMiddleware.php
@@ -9,24 +9,12 @@
 
 final class RemoteMiddleware implements Middleware
 {
-    /**
-     * @var Gateway
-     */
-    private $gateway;
-
-    /**
-     * @var array<string>
-     */
-    private $local;
-
     /**
      * @param Gateway       $gateway
      * @param array<string> $local
      */
-    public function __construct(Gateway $gateway, array $local = [])
+    public function __construct(private Gateway $gateway, private array $local = [])
     {
-        $this->gateway = $gateway;
-        $this->local   = $local;
     }
 
     /**
diff --git a/src/Remote/Serializer/NativeSerializer.php b/src/Remote/Serializer/NativeSerializer.php
index af0bbdc..ebb97cf 100644
--- a/src/Remote/Serializer/NativeSerializer.php
+++ b/src/Remote/Serializer/NativeSerializer.php
@@ -4,6 +4,7 @@
 
 namespace Onliner\CommandBus\Remote\Serializer;
 
+use Onliner\CommandBus\Exception;
 use Onliner\CommandBus\Remote\Envelope;
 use Onliner\CommandBus\Remote\Serializer;
 
@@ -22,6 +23,12 @@ public function serialize(object $command, array $headers = []): Envelope
      */
     public function unserialize(Envelope $envelope): object
     {
-        return unserialize($envelope->payload);
+        $message = unserialize($envelope->payload);
+
+        if (!$message instanceof $envelope->class) {
+            throw new Exception\InvalidMessageException($envelope->class);
+        }
+
+        return $message;
     }
 }
diff --git a/src/Remote/Transport/MemoryTransport.php b/src/Remote/Transport/MemoryTransport.php
index ca2aa30..e553836 100644
--- a/src/Remote/Transport/MemoryTransport.php
+++ b/src/Remote/Transport/MemoryTransport.php
@@ -15,19 +15,19 @@ final class MemoryTransport implements Transport, Consumer
     /**
      * @var array<string, array<Envelope>>
      */
-    private $envelopes = [];
+    private array $envelopes = [];
 
     /**
      * @var bool
      */
-    private $running = false;
+    private bool $running = false;
 
     /**
      * {@inheritDoc}
      */
     public function send(Envelope $envelope): void
     {
-        $this->envelopes[$envelope->type][] = $envelope;
+        $this->envelopes[$envelope->class][] = $envelope;
     }
 
     /**
@@ -59,7 +59,7 @@ public function run(Dispatcher $dispatcher, array $options = []): void
                     }
                 }
             }
-        } while ($this->running);
+        } while ($this->isRunning());
     }
 
     /**
@@ -95,4 +95,12 @@ public function receive(string $type): array
     {
         return $this->envelopes[$type] ?? [];
     }
+
+    /**
+     * @return bool
+     */
+    public function isRunning(): bool
+    {
+        return $this->running;
+    }
 }
diff --git a/src/Remote/Transport/MultiTransport.php b/src/Remote/Transport/MultiTransport.php
index 2721fe0..8c676d5 100644
--- a/src/Remote/Transport/MultiTransport.php
+++ b/src/Remote/Transport/MultiTransport.php
@@ -10,22 +10,16 @@
 
 class MultiTransport implements Transport
 {
-    /**
-     * @var Transport
-     */
-    private $default;
-
     /**
      * @var array<string, Transport>
      */
-    private $transports = [];
+    private array $transports = [];
 
     /**
      * @param Transport $default
      */
-    public function __construct(Transport $default)
+    public function __construct(private Transport $default)
     {
-        $this->default = $default;
     }
 
     /**
@@ -44,7 +38,7 @@ public function add(string $pattern, Transport $transport): void
      */
     public function send(Envelope $envelope): void
     {
-        $this->match($envelope->type)->send($envelope);
+        $this->match($envelope->class)->send($envelope);
     }
 
     /**
diff --git a/src/Resolver/CallableResolver.php b/src/Resolver/CallableResolver.php
index 933a81d..70e3dca 100644
--- a/src/Resolver/CallableResolver.php
+++ b/src/Resolver/CallableResolver.php
@@ -12,7 +12,7 @@ final class CallableResolver implements Resolver
     /**
      * @var array<string, callable>
      */
-    private $handlers = [];
+    private array $handlers = [];
 
     /**
      * @param string   $class
@@ -36,8 +36,6 @@ public function resolve(object $command): callable
             }
         } while ($class = get_parent_class($class));
 
-        return static function () use ($command) {
-            throw Exception\UnknownHandlerException::forCommand($command);
-        };
+        return fn () => throw new Exception\UnknownHandlerException(get_class($command));
     }
 }
diff --git a/src/Resolver/ContainerResolver.php b/src/Resolver/ContainerResolver.php
index 7a7fce8..bed8d2b 100644
--- a/src/Resolver/ContainerResolver.php
+++ b/src/Resolver/ContainerResolver.php
@@ -4,28 +4,23 @@
 
 namespace Onliner\CommandBus\Resolver;
 
+use Onliner\CommandBus\Context;
 use Onliner\CommandBus\Exception;
 use Onliner\CommandBus\Resolver;
 use Psr\Container\ContainerInterface;
 
 final class ContainerResolver implements Resolver
 {
-    /**
-     * @var ContainerInterface
-     */
-    private $container;
-
     /**
      * @var array<string, string>
      */
-    private $handlers = [];
+    private array $handlers = [];
 
     /**
      * @param ContainerInterface $container
      */
-    public function __construct(ContainerInterface $container)
+    public function __construct(private ContainerInterface $container)
     {
-        $this->container = $container;
     }
 
     /**
@@ -42,7 +37,7 @@ public function register(string $class, string $handler): void
      */
     public function resolve(object $command): callable
     {
-        return function ($command, $context) {
+        return function (object $command, Context $context) {
             $class = get_class($command);
 
             if (!isset($this->handlers[$class])) {
@@ -50,6 +45,11 @@ public function resolve(object $command): callable
             }
 
             $handler = $this->container->get($this->handlers[$class]);
+
+            if (!is_callable($handler)) {
+                throw new Exception\InvalidHandlerException($class);
+            }
+
             $handler($command, $context);
         };
     }
diff --git a/src/Resolver/MiddlewareResolver.php b/src/Resolver/MiddlewareResolver.php
index 16a5496..b6d8ab2 100644
--- a/src/Resolver/MiddlewareResolver.php
+++ b/src/Resolver/MiddlewareResolver.php
@@ -10,22 +10,16 @@
 
 final class MiddlewareResolver implements Resolver
 {
-    /**
-     * @var Resolver
-     */
-    private $resolver;
-
     /**
      * @var array<Middleware>
      */
-    private $stack = [];
+    private array $stack = [];
 
     /**
      * @param Resolver   $resolver
      */
-    public function __construct(Resolver $resolver)
+    public function __construct(private Resolver $resolver)
     {
-        $this->resolver = $resolver;
     }
 
     /**
diff --git a/src/Retry/Policy/SimplePolicy.php b/src/Retry/Policy/SimplePolicy.php
index 090ad8d..ac1d88a 100644
--- a/src/Retry/Policy/SimplePolicy.php
+++ b/src/Retry/Policy/SimplePolicy.php
@@ -12,24 +12,12 @@ final class SimplePolicy implements Policy
 {
     private const OPTION_ATTEMPT = 'attempt';
 
-    /**
-     * @var int
-     */
-    private $retries;
-
-    /**
-     * @var int
-     */
-    private $delay;
-
     /**
      * @param int $retries
      * @param int $delay
      */
-    public function __construct(int $retries, int $delay = 0)
+    public function __construct(private int $retries, private int $delay = 0)
     {
-        $this->retries = $retries;
-        $this->delay   = $delay;
     }
 
     /**
diff --git a/src/Retry/RetryExtension.php b/src/Retry/RetryExtension.php
index a7da661..c57b043 100644
--- a/src/Retry/RetryExtension.php
+++ b/src/Retry/RetryExtension.php
@@ -9,15 +9,12 @@
 
 final class RetryExtension implements Extension
 {
-    /**
-     * @var Policy
-     */
-    private $default;
+    private Policy $default;
 
     /**
      * @var array<string, Policy>
      */
-    private $policies = [];
+    private array $policies = [];
 
     /**
      * @param Policy|null $default
diff --git a/src/Retry/RetryMiddleware.php b/src/Retry/RetryMiddleware.php
index 7dab2f9..fb0794c 100644
--- a/src/Retry/RetryMiddleware.php
+++ b/src/Retry/RetryMiddleware.php
@@ -11,23 +11,11 @@
 final class RetryMiddleware implements Middleware
 {
     /**
-     * @var Policy
+     * @param Policy                $default
+     * @param array<string, Policy> $policies
      */
-    private $default;
-
-    /**
-     * @var array<string, Policy>
-     */
-    private $policies;
-
-    /**
-     * @param Policy   $default
-     * @param Policy[] $policies
-     */
-    public function __construct(Policy $default, array $policies)
+    public function __construct(private Policy $default, private array $policies)
     {
-        $this->default  = $default;
-        $this->policies = $policies;
     }
 
     /**
diff --git a/tests/ContextTest.php b/tests/ContextTest.php
index 1efc6d7..fab7c8f 100644
--- a/tests/ContextTest.php
+++ b/tests/ContextTest.php
@@ -6,7 +6,8 @@
 
 use Onliner\CommandBus\Builder;
 use Onliner\CommandBus\Context;
-use Onliner\CommandBus\Message\MessageIterator;
+use Onliner\CommandBus\Message\Deferred;
+use Onliner\CommandBus\Message\DeferredIterator;
 use Onliner\CommandBus\Tests\Command;
 use PHPUnit\Framework\TestCase;
 
@@ -19,14 +20,14 @@ public function testValues(): void
             'baz' => 1,
         ];
 
-        $context = new Context((new Builder())->build(), new MessageIterator(), $options);
+        $context = new Context((new Builder())->build(), new DeferredIterator(), $options);
 
         self::assertEquals($options, $context->all());
     }
 
     public function testOptions(): void
     {
-        $context = new Context((new Builder())->build(), new MessageIterator());
+        $context = new Context((new Builder())->build(), new DeferredIterator());
 
         self::assertEmpty($context->all());
 
@@ -71,17 +72,15 @@ public function testDispatch(): void
 
     public function testDefer(): void
     {
-        $actualDeferred = new MessageIterator();
-        $context = new Context((new Builder())->build(), $actualDeferred);
+        $iterator = new DeferredIterator();
+        $context = new Context((new Builder())->build(), $iterator);
         $context->defer(new Command\Hello('bar'));
 
-        foreach ($actualDeferred as $actualDeferredMessage) {
-            self::assertIsArray($actualDeferredMessage);
-
-            [$message, $options] = $actualDeferredMessage;
-            self::assertInstanceOf(Command\Hello::class, $message);
-            self::assertSame('bar', $message->name);
-            self::assertIsArray($options);
+        foreach ($iterator as $deferred) {
+            self::assertInstanceOf(Deferred::class, $deferred);
+            self::assertInstanceOf(Command\Hello::class, $deferred->message);
+            self::assertSame('bar', $deferred->message->name);
+            self::assertIsArray($deferred->options);
         }
     }
 }
diff --git a/tests/Remote/AMQP/AMQPTransportTest.php b/tests/Remote/AMQP/AMQPTransportTest.php
index fa9e823..98dd144 100644
--- a/tests/Remote/AMQP/AMQPTransportTest.php
+++ b/tests/Remote/AMQP/AMQPTransportTest.php
@@ -8,7 +8,9 @@
 use Onliner\CommandBus\Remote\AMQP\AMQPTransport;
 use Onliner\CommandBus\Remote\AMQP\Connector;
 use Onliner\CommandBus\Remote\AMQP\Exchange;
+use Onliner\CommandBus\Remote\AMQP\Router\SimpleRouter;
 use Onliner\CommandBus\Remote\Envelope;
+use Onliner\CommandBus\Tests\Command\Hello;
 use PhpAmqpLib\Channel\AMQPChannel;
 use PhpAmqpLib\Message\AMQPMessage;
 use PhpAmqpLib\Wire\AMQPTable;
@@ -38,12 +40,12 @@ public function testCreateWithMalformedUrl(): void
 
     public function testSend(): void
     {
-        $envelope = new Envelope('target', 'payload', [
+        $envelope = new Envelope(Hello::class, 'payload', [
             'foo' => 'bar',
         ]);
 
         $headers = $envelope->headers + [
-            'x-message-type' => $envelope->type,
+            'x-message-type' => $envelope->class,
         ];
 
         $message = new AMQPMessage($envelope->payload, [
@@ -55,7 +57,7 @@ public function testSend(): void
         $channel
             ->expects(self::exactly(2))
             ->method('basic_publish')
-            ->with($message, 'amqp.topic', $envelope->type, false, false)
+            ->with($message, 'amqp.topic', strtolower(str_replace('\\', '.', $envelope->class)), false, false)
         ;
 
         $connector = self::createMock(Connector::class);
@@ -65,7 +67,7 @@ public function testSend(): void
             ->willReturn($channel)
         ;
 
-        $transport = new AMQPTransport($connector, Exchange::create([]));
+        $transport = new AMQPTransport($connector, Exchange::create([]), new SimpleRouter());
         $transport->send($envelope);
         $transport->send($envelope);
     }
diff --git a/tests/Remote/EnvelopeTest.php b/tests/Remote/EnvelopeTest.php
index e84bc58..1ff10e3 100644
--- a/tests/Remote/EnvelopeTest.php
+++ b/tests/Remote/EnvelopeTest.php
@@ -5,13 +5,14 @@
 namespace Onliner\CommandBus\Tests\Remote;
 
 use Onliner\CommandBus\Remote\Envelope;
+use Onliner\CommandBus\Tests\Command\Hello;
 use PHPUnit\Framework\TestCase;
 
 class EnvelopeTest extends TestCase
 {
     public function testSerializeUnserialize(): void
     {
-        $target  = 'target';
+        $target  = Hello::class;
         $payload = 'payload';
         $headers = [
             'foo' => 'bar'
@@ -19,7 +20,7 @@ public function testSerializeUnserialize(): void
 
         $envelope = new Envelope($target, $payload, $headers);
 
-        self::assertSame($target, $envelope->type);
+        self::assertSame($target, $envelope->class);
         self::assertSame($payload, $envelope->payload);
         self::assertSame($headers, $envelope->headers);
     }
diff --git a/tests/Remote/GatewayTest.php b/tests/Remote/GatewayTest.php
index be312a7..eafd8d1 100644
--- a/tests/Remote/GatewayTest.php
+++ b/tests/Remote/GatewayTest.php
@@ -6,7 +6,7 @@
 
 use Onliner\CommandBus\Context;
 use Onliner\CommandBus\Dispatcher;
-use Onliner\CommandBus\Message\MessageIterator;
+use Onliner\CommandBus\Message\DeferredIterator;
 use Onliner\CommandBus\Remote\Envelope;
 use Onliner\CommandBus\Remote\Gateway;
 use Onliner\CommandBus\Remote\Serializer;
@@ -28,7 +28,7 @@ public function testSend(): void
         ];
 
         $dispatcher = new Dispatcher(new CallableResolver());
-        $context = new Context($dispatcher, new MessageIterator(), $headers);
+        $context = new Context($dispatcher, new DeferredIterator(), $headers);
 
         $gateway = new Gateway($transport, $serializer);
         $gateway->send($command, $context);
@@ -41,7 +41,7 @@ public function testSend(): void
         $envelope = reset($queue);
 
         self::assertInstanceOf(Envelope::class, $envelope);
-        self::assertSame(Hello::class, $envelope->type);
+        self::assertSame(Hello::class, $envelope->class);
         self::assertSame(serialize($command), $envelope->payload);
         self::assertSame($headers, $envelope->headers);
     }
diff --git a/tests/Remote/Transport/MemoryTransportTest.php b/tests/Remote/Transport/MemoryTransportTest.php
index 545a673..78e1295 100644
--- a/tests/Remote/Transport/MemoryTransportTest.php
+++ b/tests/Remote/Transport/MemoryTransportTest.php
@@ -6,20 +6,22 @@
 
 use Onliner\CommandBus\Remote\Envelope;
 use Onliner\CommandBus\Remote\Transport\MemoryTransport;
+use Onliner\CommandBus\Tests\Command\Hello;
 use PHPUnit\Framework\TestCase;
 
 class MemoryTransportTest extends TestCase
 {
     public function testSendReceive(): void
     {
+        $class = Hello::class;
         $transport = new MemoryTransport();
-        $envelope = new Envelope('target', 'payload', [
+        $envelope = new Envelope($class, 'payload', [
             'foo' => 'bar',
         ]);
 
         $transport->send($envelope);
 
         self::assertEquals([], $transport->receive('unknown'));
-        self::assertEquals([$envelope], $transport->receive('target'));
+        self::assertEquals([$envelope], $transport->receive($class));
     }
 }
diff --git a/tests/Resolver/MiddlewareResolverTest.php b/tests/Resolver/MiddlewareResolverTest.php
index 6f96f36..207d2e2 100644
--- a/tests/Resolver/MiddlewareResolverTest.php
+++ b/tests/Resolver/MiddlewareResolverTest.php
@@ -6,7 +6,7 @@
 
 use Onliner\CommandBus\Context;
 use Onliner\CommandBus\Dispatcher;
-use Onliner\CommandBus\Message\MessageIterator;
+use Onliner\CommandBus\Message\DeferredIterator;
 use Onliner\CommandBus\Middleware;
 use Onliner\CommandBus\Resolver;
 use Onliner\CommandBus\Tests\Command;
@@ -45,7 +45,7 @@ public function testMiddleware(): void
             ->willReturn($handler)
         ;
 
-        $context = new Context(new Dispatcher($parent), new MessageIterator());
+        $context = new Context(new Dispatcher($parent), new DeferredIterator());
 
         $middleware = self::createMock(Middleware::class);
         $middleware