diff --git a/lib/Twig/Extension/Core.php b/lib/Twig/Extension/Core.php
index 0a05a0490..60a113060 100644
--- a/lib/Twig/Extension/Core.php
+++ b/lib/Twig/Extension/Core.php
@@ -652,7 +652,7 @@ function twig_array_merge($arr1, $arr2)
 function twig_slice(Twig_Environment $env, $item, $start, $length = null, $preserveKeys = false)
 {
     if ($item instanceof Traversable) {
-        if ($item instanceof IteratorAggregate) {
+        while ($item instanceof IteratorAggregate) {
             $item = $item->getIterator();
         }
 
@@ -821,7 +821,27 @@ function _twig_default_filter($value, $default = '')
 function twig_get_array_keys_filter($array)
 {
     if ($array instanceof Traversable) {
-        return array_keys(iterator_to_array($array));
+        while ($array instanceof IteratorAggregate) {
+            $array = $array->getIterator();
+        }
+
+        if ($array instanceof Iterator) {
+            $keys = array();
+            $array->rewind();
+            while ($array->valid()) {
+                $keys[] = $array->key();
+                $array->next();
+            }
+
+            return $keys;
+        }
+
+        $keys = array();
+        foreach ($array as $key => $item) {
+            $keys[] = $key;
+        }
+
+        return $keys;
     }
 
     if (!is_array($array)) {
@@ -901,7 +921,21 @@ function twig_in_filter($value, $compare)
     } elseif (is_string($compare) && (is_string($value) || is_int($value) || is_float($value))) {
         return '' === $value || false !== strpos($compare, (string) $value);
     } elseif ($compare instanceof Traversable) {
-        return in_array($value, iterator_to_array($compare, false), is_object($value) || is_resource($value));
+        if (is_object($value) || is_resource($value)) {
+            foreach ($compare as $item) {
+                if ($item === $value) {
+                    return true;
+                }
+            }
+        } else {
+            foreach ($compare as $item) {
+                if ($item == $value) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
     }
 
     return false;
diff --git a/test/Twig/Tests/Extension/CoreTest.php b/test/Twig/Tests/Extension/CoreTest.php
index 89937b785..70312c0b9 100644
--- a/test/Twig/Tests/Extension/CoreTest.php
+++ b/test/Twig/Tests/Extension/CoreTest.php
@@ -115,14 +115,24 @@ class Twig_Tests_Extension_CoreTest extends PHPUnit_Framework_TestCase
         $this->assertEquals($output, 'éÄ');
     }
 
-    public function testCustomEscaper()
+    /**
+     * @dataProvider provideCustomEscaperCases
+     */
+    public function testCustomEscaper($expected, $string, $strategy)
     {
         $twig = new Twig_Environment($this->getMockBuilder('Twig_LoaderInterface')->getMock());
         $twig->getExtension('Twig_Extension_Core')->setEscaper('foo', 'foo_escaper_for_test');
 
-        $this->assertEquals('fooUTF-8', twig_escape_filter($twig, 'foo', 'foo'));
-        $this->assertEquals('UTF-8', twig_escape_filter($twig, null, 'foo'));
-        $this->assertEquals('42UTF-8', twig_escape_filter($twig, 42, 'foo'));
+        $this->assertSame($expected, twig_escape_filter($twig, $string, $strategy));
+    }
+
+    public function provideCustomEscaperCases()
+    {
+        return array(
+            array('fooUTF-8', 'foo', 'foo'),
+            array('UTF-8', null, 'foo'),
+            array('42UTF-8', 42, 'foo'),
+        );
     }
 
     /**
@@ -133,22 +143,129 @@ class Twig_Tests_Extension_CoreTest extends PHPUnit_Framework_TestCase
         twig_escape_filter(new Twig_Environment($this->getMockBuilder('Twig_LoaderInterface')->getMock()), 'foo', 'bar');
     }
 
-    public function testTwigFirst()
+    /**
+     * @dataProvider provideTwigFirstCases
+     */
+    public function testTwigFirst($expected, $input)
     {
         $twig = new Twig_Environment($this->getMockBuilder('Twig_LoaderInterface')->getMock());
-        $this->assertEquals('a', twig_first($twig, 'abc'));
-        $this->assertEquals(1, twig_first($twig, array(1, 2, 3)));
-        $this->assertSame('', twig_first($twig, null));
-        $this->assertSame('', twig_first($twig, ''));
+        $this->assertSame($expected, twig_first($twig, $input));
     }
 
-    public function testTwigLast()
+    public function provideTwigFirstCases()
+    {
+        $i = array(1 => 'a', 2 => 'b', 3 => 'c');
+
+        return array(
+            array('a', 'abc'),
+            array(1, array(1, 2, 3)),
+            array('', null),
+            array('', ''),
+            array('a', new CoreTestIterator($i, array_keys($i), true, 3)),
+        );
+    }
+
+    /**
+     * @dataProvider provideTwigLastCases
+     */
+    public function testTwigLast($expected, $input)
     {
         $twig = new Twig_Environment($this->getMockBuilder('Twig_LoaderInterface')->getMock());
-        $this->assertEquals('c', twig_last($twig, 'abc'));
-        $this->assertEquals(3, twig_last($twig, array(1, 2, 3)));
-        $this->assertSame('', twig_last($twig, null));
-        $this->assertSame('', twig_last($twig, ''));
+        $this->assertSame($expected, twig_last($twig, $input));
+    }
+
+    public function provideTwigLastCases()
+    {
+        $i = array(1 => 'a', 2 => 'b', 3 => 'c');
+
+        return array(
+            array('c', 'abc'),
+            array(3, array(1, 2, 3)),
+            array('', null),
+            array('', ''),
+            array('c', new CoreTestIterator($i, array_keys($i), true)),
+        );
+    }
+
+    /**
+     * @dataProvider provideArrayKeyCases
+     */
+    public function testArrayKeysFilter(array $expected, $input)
+    {
+        $this->assertSame($expected, twig_get_array_keys_filter($input));
+    }
+
+    public function provideArrayKeyCases()
+    {
+        $array = array('a' => 'a1', 'b' => 'b1', 'c' => 'c1');
+        $keys = array_keys($array);
+
+        return array(
+            array($keys, $array),
+            array($keys, new CoreTestIterator($array, $keys)),
+            array($keys, new CoreTestIteratorAggregate($array, $keys)),
+            array($keys, new CoreTestIteratorAggregateAggregate($array, $keys)),
+            array(array(), null),
+            array(array('a'), new SimpleXMLElement('<xml><a></a></xml>')),
+        );
+    }
+
+    /**
+     * @dataProvider provideInFilterCases
+     */
+    public function testInFilter($expected, $value, $compare)
+    {
+        $this->assertSame($expected, twig_in_filter($value, $compare));
+    }
+
+    public function provideInFilterCases()
+    {
+        $array = array(1, 2, 'a' => 3, 5, 6, 7);
+        $keys = array_keys($array);
+
+        return array(
+            array(true, 1, $array),
+            array(true, '3', $array),
+            array(true, '3', 'abc3def'),
+            array(true, 1, new CoreTestIterator($array, $keys, true, 1)),
+            array(true, '3', new CoreTestIterator($array, $keys, true, 3)),
+            array(true, '3', new CoreTestIteratorAggregateAggregate($array, $keys, true, 3)),
+            array(false, 4, $array),
+            array(false, 4, new CoreTestIterator($array, $keys, true)),
+            array(false, 4, new CoreTestIteratorAggregateAggregate($array, $keys, true)),
+            array(false, 1, 1),
+            array(true, 'b', new SimpleXMLElement('<xml><a>b</a></xml>')),
+        );
+    }
+
+    /**
+     * @dataProvider provideSliceFilterCases
+     */
+    public function testSliceFilter($expected, $input, $start, $length = null, $preserveKeys = false)
+    {
+        $twig = new Twig_Environment($this->getMockBuilder('Twig_LoaderInterface')->getMock());
+        $this->assertSame($expected, twig_slice($twig, $input, $start, $length, $preserveKeys));
+    }
+
+    public function provideSliceFilterCases()
+    {
+        $i = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4);
+        $keys = array_keys($i);
+
+        return array(
+            array(array('a' => 1), $i, 0, 1, true),
+            array(array('a' => 1), $i, 0, 1, false),
+            array(array('b' => 2, 'c' => 3), $i, 1, 2),
+            array(array(1), array(1, 2, 3, 4), 0, 1),
+            array(array(2, 3), array(1, 2, 3, 4), 1, 2),
+            array(array(2, 3), new CoreTestIterator($i, $keys, true), 1, 2),
+            array(array('c' => 3, 'd' => 4), new CoreTestIteratorAggregate($i, $keys, true), 2, null, true),
+            array($i, new CoreTestIterator($i, $keys, true), 0, count($keys) + 10, true),
+            array(array(), new CoreTestIterator($i, $keys, true), count($keys) + 10),
+            array('de', 'abcdef', 3, 2),
+            array(array(), new SimpleXMLElement('<items><item>1</item><item>2</item></items>'), 3),
+            array(array(), new ArrayIterator(array(1, 2)), 3)
+        );
     }
 }
 
@@ -156,3 +273,83 @@ function foo_escaper_for_test(Twig_Environment $env, $string, $charset)
 {
     return $string.$charset;
 }
+
+final class CoreTestIteratorAggregate implements IteratorAggregate
+{
+    private $iterator;
+
+    public function __construct(array $array, array $keys, $allowAccess = false, $maxPosition = false)
+    {
+        $this->iterator = new CoreTestIterator($array, $keys, $allowAccess, $maxPosition);
+    }
+
+    public function getIterator()
+    {
+        return $this->iterator;
+    }
+}
+
+final class CoreTestIteratorAggregateAggregate implements IteratorAggregate
+{
+    private $iterator;
+
+    public function __construct(array $array, array $keys, $allowValueAccess = false, $maxPosition = false)
+    {
+        $this->iterator = new CoreTestIteratorAggregate($array, $keys, $allowValueAccess, $maxPosition);
+    }
+
+    public function getIterator()
+    {
+        return $this->iterator;
+    }
+}
+
+final class CoreTestIterator implements Iterator
+{
+    private $position;
+    private $array;
+    private $arrayKeys;
+    private $allowValueAccess;
+    private $maxPosition;
+
+    public function __construct(array $values, array $keys, $allowValueAccess = false, $maxPosition = false)
+    {
+        $this->array = $values;
+        $this->arrayKeys = $keys;
+        $this->position = 0;
+        $this->allowValueAccess = $allowValueAccess;
+        $this->maxPosition = false === $maxPosition ? count($values) + 1 : $maxPosition;
+    }
+
+    public function rewind()
+    {
+        $this->position = 0;
+    }
+
+    public function current()
+    {
+        if ($this->allowValueAccess) {
+            return $this->array[$this->key()];
+        }
+
+        throw new \LogicException('Code should only use the keys, not the values provided by iterator.');
+    }
+
+    public function key()
+    {
+        return $this->arrayKeys[$this->position];
+    }
+
+    public function next()
+    {
+        ++$this->position;
+        if ($this->position === $this->maxPosition) {
+             throw new \LogicException(sprintf('Code should not iterate beyond %d.', $this->maxPosition));
+        }
+    }
+
+    public function valid()
+    {
+        return isset($this->arrayKeys[$this->position]);
+    }
+}