diff --git a/src/collections_me.c b/src/collections_me.c
index 5dd8abd..c1594aa 100644
--- a/src/collections_me.c
+++ b/src/collections_me.c
@@ -165,7 +165,7 @@ const zend_function_entry collection_methods[] = {
     PHP_ME(Collection, intersectKeys, other_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, intersectValues, other_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, isEmpty, NULL, ZEND_ACC_PUBLIC)
-    PHP_ME(Collection, isNotEmpty, NULL, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, isPacked, 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)
@@ -180,7 +180,6 @@ const zend_function_entry collection_methods[] = {
     PHP_ME(Collection, minus, elements_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, none, predicate_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, onEach, action_arginfo, ZEND_ACC_PUBLIC)
-    PHP_ME(Collection, packed, 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, putAll, elements_arginfo, ZEND_ACC_PUBLIC)
diff --git a/src/collections_methods.c b/src/collections_methods.c
index fe8a15b..bfb0d06 100644
--- a/src/collections_methods.c
+++ b/src/collections_methods.c
@@ -27,7 +27,7 @@
 #define IS_COLLECTION_P(zval)                                              \
     Z_TYPE_P(zval) == IS_OBJECT && Z_OBJCE_P(zval) == collections_collection_ce
 #define IS_PAIR(zval)                                                      \
-    EXPECTED(Z_TYPE(zval) == IS_OBJECT) && EXPECTED(Z_OBJCE(zval) == collections_pair_ce)
+    Z_TYPE(zval) == IS_OBJECT && Z_OBJCE(zval) == collections_pair_ce
 
 #define SEPARATE_COLLECTION(ht, obj)                                       \
     if (GC_REFCOUNT(ht) > 1) {                                             \
@@ -607,7 +607,7 @@ PHP_METHOD(Collection, associate)
     ARRAY_NEW_EX(new_collection, current);
     ZEND_HASH_FOREACH_BUCKET(current, Bucket* bucket)
         CALLBACK_KEYVAL_INVOKE(params, bucket);
-        if (IS_PAIR(retval)) {
+        if (EXPECTED(IS_PAIR(retval))) {
             zval* key = PAIR_FIRST(Z_OBJ(retval));
             zval* value = PAIR_SECOND(Z_OBJ(retval));
             if (Z_TYPE_P(key) == IS_LONG) {
@@ -642,7 +642,7 @@ PHP_METHOD(Collection, associateTo)
     SEPARATE_COLLECTION(dest_arr, dest);
     ZEND_HASH_FOREACH_BUCKET(current, Bucket* bucket)
         CALLBACK_KEYVAL_INVOKE(params, bucket);
-        if (IS_PAIR(retval)) {
+        if (EXPECTED(IS_PAIR(retval))) {
             zval* key = PAIR_FIRST(Z_OBJ(retval));
             zval* value = PAIR_SECOND(Z_OBJ(retval));
             if (Z_TYPE_P(key) == IS_LONG) {
@@ -738,19 +738,15 @@ PHP_METHOD(Collection, containsAll)
     ZEND_PARSE_PARAMETERS_END();
     ELEMENTS_VALIDATE(elements, ERR_BAD_ARGUMENT_TYPE, return);
     zend_array* current = COLLECTION_FETCH_CURRENT();
-    equal_check_func_t eql = NULL;
     ZEND_HASH_FOREACH_BUCKET(elements_arr, Bucket* bucket)
-        if (UNEXPECTED(eql == NULL)) {
-            eql = equal_check_func_init(&bucket->val);
-        }
         if (bucket->key) {
             zval* result = zend_hash_find(current, bucket->key);
-            if (!result || !eql(&bucket->val, result)) {
+            if (!result || !fast_equal_check_function(&bucket->val, result)) {
                 RETURN_FALSE;
             }
         } else {
             zval* result = zend_hash_index_find(current, bucket->h);
-            if (!result || !eql(&bucket->val, result)) {
+            if (!result || !fast_equal_check_function(&bucket->val, result)) {
                 RETURN_FALSE;
             }
         }
@@ -1465,7 +1461,7 @@ PHP_METHOD(Collection, groupBy)
         CALLBACK_KEYVAL_INVOKE(params, bucket);
         zval* key;
         zval* value;
-        if (IS_PAIR(retval)) {
+        if (EXPECTED(IS_PAIR(retval))) {
             key = PAIR_FIRST(Z_OBJ(retval));
             value = PAIR_SECOND(Z_OBJ(retval));
         } else {
@@ -1507,7 +1503,7 @@ PHP_METHOD(Collection, groupByTo)
         CALLBACK_KEYVAL_INVOKE(params, bucket);
         zval* key;
         zval* value;
-        if (IS_PAIR(retval)) {
+        if (EXPECTED(IS_PAIR(retval))) {
             key = PAIR_FIRST(Z_OBJ(retval));
             value = PAIR_SECOND(Z_OBJ(retval));
         } else {
@@ -1680,10 +1676,10 @@ PHP_METHOD(Collection, isEmpty)
     RETVAL_BOOL(zend_hash_num_elements(current) == 0);
 }
 
-PHP_METHOD(Collection, isNotEmpty)
+PHP_METHOD(Collection, isPacked)
 {
     zend_array* current = COLLECTION_FETCH_CURRENT();
-    RETVAL_BOOL(zend_hash_num_elements(current));
+    RETVAL_BOOL(HT_IS_PACKED(current));
 }
 
 PHP_METHOD(Collection, keys)
@@ -1947,7 +1943,31 @@ PHP_METHOD(Collection, minWith)
 
 PHP_METHOD(Collection, minus)
 {
-    
+    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(new_collection, 8);
+    ZEND_HASH_FOREACH_BUCKET(current, Bucket* bucket)
+        zval* result;
+        if (bucket->key) {
+            result = zend_hash_find(elements_arr, bucket->key);
+        } else {
+            result = zend_hash_index_find(elements_arr, bucket->h);
+        }
+        if (result && fast_equal_check_function(result, &bucket->val)) {
+            continue;
+        }
+        Z_TRY_ADDREF(bucket->val);
+        if (bucket->key) {
+            zend_hash_add(new_collection, bucket->key, &bucket->val);
+        } else {
+            zend_hash_index_add(new_collection, bucket->h, &bucket->val);
+        }
+    ZEND_HASH_FOREACH_END();
+    RETVAL_NEW_COLLECTION(new_collection);
 }
 
 PHP_METHOD(Collection, none)
@@ -1986,12 +2006,6 @@ PHP_METHOD(Collection, onEach)
     RETVAL_ZVAL(getThis(), 1, 0);
 }
 
-PHP_METHOD(Collection, packed)
-{
-    zend_array* current = COLLECTION_FETCH_CURRENT();
-    RETVAL_BOOL(HT_IS_PACKED(current));
-}
-
 PHP_METHOD(Collection, partition)
 {
     zend_fcall_info fci;
@@ -2274,6 +2288,11 @@ PHP_METHOD(Collection, shuffle)
     } else {
         zend_array_destroy(current);
     }
+    if (GC_REFCOUNT(current) > 1) {
+        GC_DELREF(current);
+    } else {
+        zend_array_destroy(current);
+    }
     COLLECTION_FETCH_CURRENT() = shuffled;
 }
 
diff --git a/src/php_collections_me.h b/src/php_collections_me.h
index efa9840..3c53ceb 100644
--- a/src/php_collections_me.h
+++ b/src/php_collections_me.h
@@ -53,7 +53,7 @@ PHP_METHOD(Collection, intersect);
 PHP_METHOD(Collection, intersectKeys);
 PHP_METHOD(Collection, intersectValues);
 PHP_METHOD(Collection, isEmpty);
-PHP_METHOD(Collection, isNotEmpty);
+PHP_METHOD(Collection, isPacked);
 PHP_METHOD(Collection, keys);
 PHP_METHOD(Collection, last);
 PHP_METHOD(Collection, lastIndexOf);
@@ -68,7 +68,6 @@ PHP_METHOD(Collection, minWith);
 PHP_METHOD(Collection, minus);
 PHP_METHOD(Collection, none);
 PHP_METHOD(Collection, onEach);
-PHP_METHOD(Collection, packed);
 PHP_METHOD(Collection, partition);
 PHP_METHOD(Collection, plus);
 PHP_METHOD(Collection, putAll);
diff --git a/stubs/Collection.php b/stubs/Collection.php
index 72f4da1..b6225f8 100644
--- a/stubs/Collection.php
+++ b/stubs/Collection.php
@@ -425,11 +425,11 @@ class Collection implements ArrayAccess, Countable
     function isEmpty() {}
 
     /**
-     * Returns true if the collection is not empty.
-     * 
+     * Check whether the collection wraps a packed hashtable (regular array).
+     *
      * @return bool
      */
-    function isNotEmpty() {}
+    function isPacked() {}
 
     /**
      * Return a collection of all keys in the collection.
@@ -587,13 +587,6 @@ class Collection implements ArrayAccess, Countable
      */
     function onEach($action) {}
 
-    /**
-     * Check whether the collection wraps a packed hashtable (regular array).
-     *
-     * @return bool
-     */
-    function packed() {}
-
     /**
      * Splits the original collection into pair of collections, where first collection contains
      * elements for which predicate yielded true, while second collection contains elements for
diff --git a/tests/026-is-empty.phpt b/tests/026-is-empty.phpt
index 81230ca..507f877 100644
--- a/tests/026-is-empty.phpt
+++ b/tests/026-is-empty.phpt
@@ -1,11 +1,11 @@
 --TEST--
-Test Collection::isEmpty() and Collection::isNotEmpty().
+Test Collection::isEmpty().
 --FILE--
 <?php
 if (!Collection::init()->isEmpty()) {
     echo 'Collection::isEmpty() failed.', PHP_EOL;
 }
-if (!Collection::init(['foo', 'bar'])->isNotEmpty()) {
+if (Collection::init(['foo', 'bar'])->isEmpty()) {
     echo 'Collection::isNotEmpty() failed.', PHP_EOL;
 }
 ?>
diff --git a/tests/040-is-packed.phpt b/tests/040-is-packed.phpt
new file mode 100644
index 0000000..153e9a0
--- /dev/null
+++ b/tests/040-is-packed.phpt
@@ -0,0 +1,12 @@
+--TEST--
+Test Collection::isPacked().
+--FILE--
+<?php
+$case = Collection::init(['a', 'b', 'c'])->isPacked();
+$case1 = Collection::init(['foo' => 'bar', 'baz'])->isPacked();
+$case2 = Collection::init()->isPacked();
+if (!$case || $case1 || $case2) {
+    echo 'Collection::isPacked() failed.', PHP_EOL;
+}
+?>
+--EXPECT--
diff --git a/tests/040-packed.phpt b/tests/040-packed.phpt
deleted file mode 100644
index 2910a73..0000000
--- a/tests/040-packed.phpt
+++ /dev/null
@@ -1,12 +0,0 @@
---TEST--
-Test Collection::packed().
---FILE--
-<?php
-$case = Collection::init(['a', 'b', 'c'])->packed();
-$case1 = Collection::init(['foo' => 'bar', 'baz'])->packed();
-$case2 = Collection::init()->packed();
-if (!$case || $case1 || $case2) {
-    echo 'Collection::packed() failed.', PHP_EOL;
-}
-?>
---EXPECT--
diff --git a/tests/053-minus.phpt b/tests/053-minus.phpt
new file mode 100644
index 0000000..c4552c0
--- /dev/null
+++ b/tests/053-minus.phpt
@@ -0,0 +1,22 @@
+--TEST--
+Test Collection::minus().
+--FILE--
+<?php
+$array = [
+    'a' => 'b',
+    'c' => 'd',
+    'e' => 'f'
+];
+$array1 = [
+    'a' => 'g',
+    'c' => 'd',
+    'h' => 'f'
+];
+$collection = Collection::init($array);
+$collection1 = Collection::init($array1);
+$subtraction = array_diff_assoc($array, $array1);
+if ($collection->minus($collection1)->toArray() != $subtraction) {
+    echo 'Collection::minus() failed.', PHP_EOL;
+}
+?>
+--EXPECT--