Add Promise\wrap (#234)

lib/functions.php

@@ -287,7 +287,7 @@ namespace Amp\Promise
      * This function is the same as some() with the notable exception that it will never fail even
      * if all promises in the array resolve unsuccessfully.
      *
-     * @param Promise[] $promises
+     * @param \Amp\Promise[]|\React\Promise\PromiseInterface[] $promises
      *
      * @return \Amp\Promise
      *
@@ -303,7 +303,7 @@ namespace Amp\Promise
      * promise succeeds with an array of values used to succeed each contained promise, with keys corresponding to
      * the array of promises.
      *
-     * @param \Amp\Promise[] $promises Array of only promises.
+     * @param \Amp\Promise[]|\React\Promise\PromiseInterface[] $promises Array of only promises.
      *
      * @return \Amp\Promise
      *
@@ -354,7 +354,7 @@ namespace Amp\Promise
     /**
      * Returns a promise that succeeds when the first promise succeeds, and fails only if all promises fail.
      *
-     * @param \Amp\Promise[] $promises Array of only promises.
+     * @param \Amp\Promise[]|\React\Promise\PromiseInterface[] $promises Array of only promises.
      *
      * @return \Amp\Promise
      *
@@ -407,7 +407,7 @@ namespace Amp\Promise
      *
      * The returned promise will only fail if the given number of required promises fail.
      *
-     * @param \Amp\Promise[] $promises Array of only promises.
+     * @param \Amp\Promise[]|\React\Promise\PromiseInterface[] $promises Array of only promises.
      * @param int            $required Number of promises that must succeed for the returned promise to succeed.
      *
      * @return \Amp\Promise
@@ -471,6 +471,38 @@ namespace Amp\Promise
 
         return $result;
     }
+
+    /**
+     * Wraps a promise into another promise, altering the exception or result.
+     *
+     * @param \Amp\Promise|\React\Promise\PromiseInterface $promise
+     * @param callable $callback
+     * @return Promise
+     */
+    function wrap($promise, callable $callback): Promise
+    {
+        if ($promise instanceof ReactPromise) {
+            $promise = adapt($promise);
+        } elseif (!$promise instanceof Promise) {
+            throw createTypeError([Promise::class, ReactPromise::class], $promise);
+        }
+
+        $deferred = new Deferred();
+
+        $promise->onResolve(function (\Throwable $exception = null, $result) use ($deferred, $callback) {
+            try {
+                $result = $callback($exception, $result);
+            } catch (\Throwable $exception) {
+                $deferred->fail($exception);
+
+                return;
+            }
+
+            $deferred->resolve($result);
+        });
+
+        return $deferred->promise();
+    }
 }
 
 namespace Amp\Iterator

test/WrapTest.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace Amp\Test;
+
+use Amp\Deferred;
+use Amp\Promise;
+
+class WrapTest extends \PHPUnit\Framework\TestCase
+{
+    public function testSuccess()
+    {
+        $deferred = new Deferred();
+
+        $promise = Promise\wrap($deferred->promise(), function () {
+            return 2;
+        });
+
+        $deferred->resolve(1);
+
+        $result = Promise\wait($promise);
+
+        $this->assertSame(2, $result);
+    }
+
+    /**
+     * @expectedException \Exception
+     * @expectedExceptionMessage bar
+     */
+    public function testFailure()
+    {
+        $deferred = new Deferred();
+
+        $promise = Promise\wrap($deferred->promise(), function () {
+            throw new \Exception('bar');
+        });
+
+        $deferred->fail(new \Exception('foo'));
+
+        Promise\wait($promise);
+    }
+}