Use call in LazyPromise and make class final

lib/LazyPromise.php

@@ -2,22 +2,21 @@
 
 namespace Amp;
 
-use React\Promise\PromiseInterface as ReactPromise;
-
 /**
  * Creates a promise that calls $promisor only when the result of the promise is requested (i.e. onResolve() is called
  * on the promise). $promisor can return a promise or any value. If $promisor throws an exception, the promise fails
- * with that exception.
+ * with that exception. If $promisor returns a Generator, it will be run as a coroutine.
  */
-class LazyPromise implements Promise {
+final class LazyPromise implements Promise {
     /** @var callable|null */
     private $promisor;
 
     /** @var \Amp\Promise|null */
     private $promise;
 
     /**
-     * @param callable $promisor Function which starts an async operation, returning a Promise or any value.
+     * @param callable $promisor Function which starts an async operation, returning a Promise (or any value).
+     *     Generators will be run as a coroutine.
      */
     public function __construct(callable $promisor) {
         $this->promisor = $promisor;
@@ -30,20 +29,7 @@ public function onResolve(callable $onResolved) {
         if ($this->promise === null) {
             $provider = $this->promisor;
             $this->promisor = null;
-
-            try {
-                $this->promise = $provider();
-
-                if ($this->promise instanceof \Generator) {
-                    $this->promise = new Coroutine($this->promise);
-                } elseif ($this->promise instanceof ReactPromise) {
-                    $this->promise = Promise\adapt($this->promise);
-                } elseif (!$this->promise instanceof Promise) {
-                    $this->promise = new Success($this->promise);
-                }
-            } catch (\Throwable $exception) {
-                $this->promise = new Failure($exception);
-            }
+            $this->promise = call($provider);
         }
 
         $this->promise->onResolve($onResolved);