Add readonly where applicable

src/DeferredCancellation.php

@@ -37,8 +37,8 @@ namespace Amp;
  */
 final class DeferredCancellation
 {
-    private Internal\Cancellable $source;
-    private Cancellation $cancellation;
+    private readonly Internal\Cancellable $source;
+    private readonly Cancellation $cancellation;
 
     public function __construct()
     {

src/DeferredFuture.php

@@ -8,10 +8,10 @@ namespace Amp;
 final class DeferredFuture
 {
     /** @var Internal\FutureState<T> */
-    private Internal\FutureState $state;
+    private readonly Internal\FutureState $state;
 
     /** @var Future<T> */
-    private Future $future;
+    private readonly Future $future;
 
     public function __construct()
     {

src/Future.php

@@ -86,7 +86,7 @@ final class Future
     }
 
     /** @var FutureState<T> */
-    private FutureState $state;
+    private readonly FutureState $state;
 
     /**
      * @param FutureState<T> $state

src/Internal/FutureIterator.php

@@ -18,11 +18,11 @@ final class FutureIterator
     /**
      * @var FutureIteratorQueue<Tk, Tv>
      */
-    private FutureIteratorQueue $queue;
+    private readonly FutureIteratorQueue $queue;
 
-    private Cancellation $cancellation;
+    private readonly Cancellation $cancellation;
 
-    private string $cancellationId;
+    private readonly string $cancellationId;
 
     /**
      * @var Future<null>|Future<never>|null

src/Internal/WrappedCancellation.php

@@ -10,7 +10,7 @@ use Amp\Cancellation;
 final class WrappedCancellation implements Cancellation
 {
     public function __construct(
-        private Cancellation $cancellation
+        private readonly Cancellation $cancellation
     ) {
     }
 

src/TimeoutCancellation.php

@@ -9,9 +9,9 @@ use Revolt\EventLoop;
  */
 final class TimeoutCancellation implements Cancellation
 {
-    private string $watcher;
+    private readonly string $watcher;
 
-    private Cancellation $cancellation;
+    private readonly Cancellation $cancellation;
 
     /**
      * @param float  $timeout Seconds until cancellation is requested.