HHVM does not allow array_walk on ArrayObject instances

tests/GridFS/SpecFunctionalTest.php

@@ -97,21 +97,19 @@ class SpecFunctionalTest extends FunctionalTestCase
         foreach ($mi as $documents) {
             list($expectedDocument, $actualDocument) = $documents;
 
-            array_walk($expectedDocument, function(&$value) use ($actualResult) {
-                if ($value === '*result') {
-                    $value = $actualResult;
+            foreach ($expectedDocument as $key => $value) {
+                if ( ! is_string($value)) {
+                    continue;
                 }
-            });
 
-            array_walk($expectedDocument, function(&$value, $key) use ($actualDocument) {
-                if ( ! is_string($value)) {
-                    return;
+                if ($value === '*result') {
+                    $expectedDocument[$key] = $actualResult;
                 }
 
                 if ( ! strncmp($value, '*actual_', 8)) {
-                    $value = $actualDocument[$key];
+                    $expectedDocument[$key] = $actualDocument[$key];
+                }
             }
-            });
 
             $this->assertSameDocument($expectedDocument, $actualDocument);
         }