Implement dummy cancellation for settled promises

Author: clue

README.md

@@ -504,6 +504,11 @@ further interest in the results of the operation.
 Once a promise is settled (either resolved or rejected), calling `cancel()` on
 a promise has no effect.
 
+#### Implementations
+
+* [FulfilledPromise](#fulfilledpromise)
+* [RejectedPromise](#rejectedpromise)
+
 Examples
 --------
 

src/React/Promise/FulfilledPromise.php

@@ -2,7 +2,7 @@
 
 namespace React\Promise;
 
-class FulfilledPromise implements PromiseInterface
+class FulfilledPromise implements PromiseInterface, CancellablePromiseInterface
 {
     private $result;
 
@@ -27,4 +27,8 @@ public function then($fulfilledHandler = null, $errorHandler = null, $progressHa
             return new RejectedPromise($exception);
         }
     }
+
+    public function cancel()
+    {
+    }
 }

src/React/Promise/RejectedPromise.php

@@ -2,7 +2,7 @@
 
 namespace React\Promise;
 
-class RejectedPromise implements PromiseInterface
+class RejectedPromise implements PromiseInterface, CancellablePromiseInterface
 {
     private $reason;
 
@@ -27,4 +27,8 @@ public function then($fulfilledHandler = null, $errorHandler = null, $progressHa
             return new RejectedPromise($exception);
         }
     }
+
+    public function cancel()
+    {
+    }
 }

tests/React/Promise/FulfilledPromiseTest.php

@@ -140,4 +140,12 @@ public function shouldSwitchFromCallbacksToErrbacksWhenCallbackThrows()
                 $mock2
             );
     }
+
+    /** @test */
+    public function shouldNotBeAffectedByCancellation()
+    {
+        $p = new FulfilledPromise(1);
+        $p->cancel();
+        $p->then($this->expectCallableOnce());
+    }
 }

tests/React/Promise/RejectedPromiseTest.php

@@ -145,4 +145,12 @@ function ($val) {
                 $mock
             );
     }
+
+    /** @test */
+    public function shouldNotBeAffectedByCancellation()
+    {
+        $p = new RejectedPromise(1);
+        $p->cancel();
+        $p->then($this->expectCallableNever(), $this->expectCallableOnce());
+    }
 }