Add `slice()`.

src/collections_methods.c

@@ -1419,7 +1419,29 @@ PHP_METHOD(Collection, single)
 
 PHP_METHOD(Collection, slice)
 {
-    
+    zval* elements;
+    ZEND_PARSE_PARAMETERS_START(1, 1)
+        Z_PARAM_ZVAL(elements)
+    ZEND_PARSE_PARAMETERS_END();
+    ELEMENTS_VALIDATE(elements, ERR_BAD_ARGUMENT_TYPE, return);
+    zend_array* current = COLLECTION_FETCH_CURRENT();
+    ARRAY_NEW_EX(sliced, current);
+    ZEND_HASH_FOREACH_VAL(elements_arr, zval* val)
+        if (Z_TYPE_P(val) == IS_LONG) {
+            zval* found = zend_hash_index_find(current, Z_LVAL_P(val));
+            if (found) {
+                Z_TRY_ADDREF_P(found);
+                zend_hash_next_index_insert(sliced, found);
+            }
+        } else if (Z_TYPE_P(val) == IS_STRING) {
+            zval* found = zend_hash_find(current, Z_STR_P(val));
+            if (found) {
+                Z_TRY_ADDREF_P(found);
+                zend_hash_add(sliced, Z_STR_P(val), found);
+            }
+        }
+    ZEND_HASH_FOREACH_END();
+    RETVAL_NEW_COLLECTION(sliced);
 }
 
 PHP_METHOD(Collection, sort)

stubs/Collection.php

@@ -745,6 +745,7 @@ class Collection implements ArrayAccess, Countable
      * Returns a list containing elements at specified keys.
      *
      * @param array|Collection $keys
+     * @return Collection
      */
     function slice($keys) {}
 

tests/036-slice.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Test Collection::slice().
+--FILE--
+<?php
+$array = [1, 2, 3, 4, 5, 6];
+$collection = Collection::init($array)->slice([2, -1, 3, 6]);
+$array1 = ['a' => 'b', 'c' => 'd', 'e' => 'f'];
+$collection1 = Collection::init($array1)->slice(['c', 'a', 'g']);
+if ($collection->toArray() != [3, 4] || $collection1->toArray() != ['c' => 'd', 'a' => 'b'])
+    echo 'Collection::slice() failed.', PHP_EOL;
+?>
+--EXPECT--