diff --git a/collections_fe.c b/collections_fe.c
index f7e38b9..6f6e84e 100644
--- a/collections_fe.c
+++ b/collections_fe.c
@@ -12,6 +12,20 @@ ZEND_BEGIN_ARG_INFO(action_arginfo, 0)
     ZEND_ARG_CALLABLE_INFO(0, action, 0)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_INFO(comparator_arginfo, 0)
+    ZEND_ARG_CALLABLE_INFO(0, comparator, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(destination_predicate_arginfo, 0)
+    ZEND_ARG_OBJ_INFO(0, destination, Collection, 0)
+    ZEND_ARG_CALLABLE_INFO(0, predicate, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(destination_transform_arginfo, 0)
+    ZEND_ARG_OBJ_INFO(0, destination, Collection, 0)
+    ZEND_ARG_CALLABLE_INFO(0, tranform, 0)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_INFO(element_arginfo, 0)
     ZEND_ARG_INFO(0, element)
 ZEND_END_ARG_INFO()
@@ -20,6 +34,29 @@ ZEND_BEGIN_ARG_INFO(elements_arginfo, 0)
     ZEND_ARG_INFO(0, elements)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_INFO(from_to_arginfo, 0)
+    ZEND_ARG_TYPE_INFO(0, from_index, IS_LONG, 0)
+    ZEND_ARG_TYPE_INFO(0, to_index, IS_LONG, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(initial_operation_arginfo, 0)
+    ZEND_ARG_INFO(0, initial)
+    ZEND_ARG_CALLABLE_INFO(0, operation, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(key_arginfo, 0)
+    ZEND_ARG_INFO(0, key)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(keys_arginfo, 0)
+    ZEND_ARG_INFO(0, keys)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(key_value_arginfo, 0)
+    ZEND_ARG_INFO(0, key)
+    ZEND_ARG_INFO(0, value)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_INFO(n_arginfo, 0)
     ZEND_ARG_TYPE_INFO(0, n, IS_LONG, 0)
 ZEND_END_ARG_INFO()
@@ -32,6 +69,10 @@ ZEND_BEGIN_ARG_INFO(selector_arginfo, 0)
     ZEND_ARG_CALLABLE_INFO(0, selector, 0)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_INFO(operation_arginfo, 0)
+    ZEND_ARG_CALLABLE_INFO(0, operation, 0)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_INFO(other_arginfo, 0)
     ZEND_ARG_INFO(0, other)
 ZEND_END_ARG_INFO()
@@ -49,21 +90,38 @@ ZEND_BEGIN_ARG_INFO(associate_by_to_arginfo, 0)
     ZEND_ARG_CALLABLE_INFO(0, key_selector, 0)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_INFO(contains_key_arginfo, 0)
-    ZEND_ARG_INFO(0, key)
-ZEND_END_ARG_INFO()
-
 ZEND_BEGIN_ARG_INFO(copy_of_arginfo, 0)
     ZEND_ARG_INFO(0, elements)
     ZEND_ARG_TYPE_INFO(0, new_size, IS_LONG, 0)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_INFO(copy_of_range_arginfo, 0)
+ZEND_BEGIN_ARG_INFO(fill_arginfo, 0)
+    ZEND_ARG_INFO(0, element)
     ZEND_ARG_TYPE_INFO(0, from_index, IS_LONG, 0)
     ZEND_ARG_TYPE_INFO(0, to_index, IS_LONG, 0)
 ZEND_END_ARG_INFO()
 
-const zend_function_entry collections_collection_methods[] = {
+ZEND_BEGIN_ARG_INFO(get_arginfo, 0)
+    ZEND_ARG_INFO(0, key)
+    ZEND_ARG_INFO(0, default)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(group_by_arginfo, 0)
+    ZEND_ARG_CALLABLE_INFO(0, key_selector, 0)
+    ZEND_ARG_CALLABLE_INFO(0, value_transform, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(group_by_to_arginfo, 0)
+    ZEND_ARG_OBJ_INFO(0, destination, Collection, 0)
+    ZEND_ARG_CALLABLE_INFO(0, key_selector, 0)
+    ZEND_ARG_CALLABLE_INFO(0, value_transform, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_INFO(to_collection_arginfo, 0)
+    ZEND_ARG_OBJ_INFO(0, destination, Collection, 0)
+ZEND_END_ARG_INFO()
+
+const zend_function_entry collection_methods[] = {
     PHP_ME(Collection, __construct, NULL, ZEND_ACC_PRIVATE | ZEND_ACC_CTOR)
     PHP_ME(Collection, addAll, elements_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, all, predicate_arginfo, ZEND_ACC_PUBLIC)
@@ -73,18 +131,108 @@ const zend_function_entry collections_collection_methods[] = {
     PHP_ME(Collection, associateByTo, associate_by_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, average, NULL, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, containsAll, other_arginfo, ZEND_ACC_PUBLIC)
-    PHP_ME(Collection, containsKey, contains_key_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, containsKey, key_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, containsValue, element_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, copyOf, copy_of_arginfo, ZEND_ACC_PUBLIC)
-    PHP_ME(Collection, copyOfRange, copy_of_range_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, copyOfRange, from_to_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, count, NULL, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, distinct, NULL, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, distinctBy, selector_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, drop, n_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, dropLast, n_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, dropLastWhile, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, dropWhile, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, fill, fill_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, filter, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, filterNot, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, filterNotTo, destination_predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, filterTo, destination_predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, find, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, findLast, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, first, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, flatMap, transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, flatMapTo, destination_transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, flatten, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, fold, initial_operation_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, foldRight, initial_operation_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, forEach, action_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, get, get_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, groupBy, group_by_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, groupByTo, group_by_to_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, indexOf, element_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, indexOfFirst, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, indexOfLast, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, init, elements_arginfo, ZEND_ACC_PUBLIC | ZEND_ACC_STATIC)
+    PHP_ME(Collection, intersect, other_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, isEmpty, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, isNotEmpty, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, keys, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, last, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, lastIndexOf, element_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, map, transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, mapKeys, transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, mapKeysTo, destination_transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, mapTo, destination_transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, mapValues, transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, mapValuesTo, destination_transform_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, max, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, maxBy, selector_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, maxWith, comparator_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, min, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minBy, selector_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minWith, comparator_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minus, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minusAssign, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minusKeys, keys_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minusKeysAssign, keys_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minusValues, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, minusValuesAssign, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, none, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, offsetUnset, key_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, offsetSet, key_value_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, offsetExists, key_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, onEach, action_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, orEmpty, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, partition, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, plus, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, plusAssign, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, plusValues, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, plusValuesAssign, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, putAll, elements_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, reduce, operation_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, reduceRight, operation_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, remove, key_value_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, removeAll, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, retainAll, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, reverse, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, reversed, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, shuffle, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, single, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, slice, keys_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sliceRange, from_to_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sort, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortBy, selector_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortByDescending, selector_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortDescending, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortWith, comparator_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sorted, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortedBy, selector_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortedByDescending, selector_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortedDescending, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, sortedWith, comparator_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, take, n_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, takeLast, n_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, takeLastWhile, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, takeWhile, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, toArray, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, toCollection, to_collection_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, toPairs, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, union, other_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, values, NULL, ZEND_ACC_PUBLIC)
     PHP_FE_END
 };
 
-const zend_function_entry collections_pair_methods[] = {
+const zend_function_entry pair_methods[] = {
+    PHP_ME(Pair, __construct, key_value_arginfo, ZEND_ACC_PUBLIC | ZEND_ACC_CTOR)
     PHP_FE_END
 };
\ No newline at end of file
diff --git a/php_collections.h b/php_collections.h
index c9273b1..5768651 100644
--- a/php_collections.h
+++ b/php_collections.h
@@ -13,8 +13,8 @@ extern zend_module_entry collections_module_entry;
 extern zend_class_entry collections_collection_ce;
 extern zend_class_entry collections_pair_ce;
 
-const zend_function_entry collection_methods[];
-const zend_function_entry pair_methods[];
+extern const zend_function_entry collection_methods[];
+extern const zend_function_entry pair_methods[];
 
 #define PHP_COLLECTIONS_VERSION "0.1.0"
 
diff --git a/php_collections_fe.h b/php_collections_fe.h
index 3d010cd..ba2b185 100644
--- a/php_collections_fe.h
+++ b/php_collections_fe.h
@@ -9,8 +9,6 @@
 
 #include <php.h>
 
-#include "php_collections.h"
-
 PHP_METHOD(Collection, __construct);
 PHP_METHOD(Collection, addAll);
 PHP_METHOD(Collection, all);
@@ -100,6 +98,7 @@ PHP_METHOD(Collection, reversed);
 PHP_METHOD(Collection, shuffle);
 PHP_METHOD(Collection, single);
 PHP_METHOD(Collection, slice);
+PHP_METHOD(Collection, sliceRange);
 PHP_METHOD(Collection, sort);
 PHP_METHOD(Collection, sortBy);
 PHP_METHOD(Collection, sortByDescending);
@@ -120,4 +119,6 @@ PHP_METHOD(Collection, toPairs);
 PHP_METHOD(Collection, union);
 PHP_METHOD(Collection, values);
 
+PHP_METHOD(Pair, __construct);
+
 #endif // !PHP_COLLECTIONS_FE_H
diff --git a/stubs/Collection.php b/stubs/Collection.php
index f8f754e..8832f05 100644
--- a/stubs/Collection.php
+++ b/stubs/Collection.php
@@ -228,7 +228,7 @@ class Collection implements ArrayAccess, Countable
      * Returns the first element matching the given predicate, or null if no such
      * element was found.
      *
-     * @param callable $predicate ($value) -> bool
+     * @param callable $predicate ($value, $key) -> bool
      * @return mixed
      */
     function find($predicate) {}
@@ -237,7 +237,7 @@ class Collection implements ArrayAccess, Countable
      * Returns the last element matching the given predicate, or null if no such
      * element was found.
      *
-     * @param callable $predicate ($value) -> bool
+     * @param callable $predicate ($value, $key) -> bool
      * @return mixed
      */
     function findLast($predicate) {}
@@ -366,10 +366,10 @@ class Collection implements ArrayAccess, Countable
     /**
      * Initialize collection with given data.
      *
-     * @param array $data[$optional]
+     * @param array|Collection $elements[$optional]
      * @return Collection
      */
-    static function init($data) {}
+    static function init($elements) {}
 
     /**
      * Returns a collection containing all elements that are contained by both this collection and the
@@ -584,22 +584,22 @@ class Collection implements ArrayAccess, Countable
     /**
      * @internal
      */
-    function offsetUnset($offset) {}
+    function offsetUnset($key) {}
 
     /**
      * @internal
      */
-    function offsetSet($offset, $value) {}
+    function offsetSet($key, $value) {}
 
     /**
      * @internal
      */
-    function offsetGet($offset) {}
+    function offsetGet($key) {}
 
     /**
      * @internal
      */
-    function offsetExists($offset) {}
+    function offsetExists($key) {}
 
     /**
      * Performs the given action on each element and returns the collection itself afterwards.
@@ -741,11 +741,19 @@ class Collection implements ArrayAccess, Countable
     function single($predicate) {}
 
     /**
-     * Returns a list containing elements at specified indices.
+     * Returns a list containing elements at specified keys.
      *
-     * @param array|Collection $indices
+     * @param array|Collection $keys
      */
-    function slice($indices) {}
+    function slice($keys) {}
+
+    /**
+     * Returns a collection containing elements at indices in the specified indices range.
+     *
+     * @param int $from_index
+     * @param int $to_index[optional]
+     */
+    function sliceRange($from_index, $to_index) {}
 
     /**
      * Sorts the collection in-place according to the natural order of its elements.