[libc++][NFC] Replace enable_if with __enable_if_t in a few places

Reviewed By: ldionne, #libc

Spies: jloser, libcxx-commits

Differential Revision: https://reviews.llvm.org/D128400

12 files changed, 77 insertions, 164 deletions

diff --git a/libcxx/include/__hash_table b/libcxx/include/__hash_table
index 20223014432f..036b0dcadc71 100644
--- a/libcxx/include/__hash_table
+++ b/libcxx/include/__hash_table
@@ -178,16 +178,14 @@ struct __hash_key_value_types<__hash_value_type<_Key, _Tp> > {
 
   template <class _Up>
   _LIBCPP_INLINE_VISIBILITY
-  static typename enable_if<__is_same_uncvref<_Up, __node_value_type>::value,
-      __container_value_type const&>::type
+  static __enable_if_t<__is_same_uncvref<_Up, __node_value_type>::value, __container_value_type const&>
   __get_value(_Up& __t) {
     return __t.__get_value();
   }
 
   template <class _Up>
   _LIBCPP_INLINE_VISIBILITY
-  static typename enable_if<__is_same_uncvref<_Up, __container_value_type>::value,
-      __container_value_type const&>::type
+  static __enable_if_t<__is_same_uncvref<_Up, __container_value_type>::value, __container_value_type const&>
   __get_value(_Up& __t) {
     return __t;
   }
@@ -1049,10 +1047,8 @@ public:
 
     template <class _First, class _Second>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<
-        __can_extract_map_key<_First, key_type, __container_value_type>::value,
-        pair<iterator, bool>
-    >::type __emplace_unique(_First&& __f, _Second&& __s) {
+    __enable_if_t<__can_extract_map_key<_First, key_type, __container_value_type>::value, pair<iterator, bool> >
+    __emplace_unique(_First&& __f, _Second&& __s) {
         return __emplace_unique_key_args(__f, _VSTD::forward<_First>(__f),
                                               _VSTD::forward<_Second>(__s));
     }
@@ -1096,9 +1092,7 @@ public:
       return __emplace_unique_key_args(_NodeTypes::__get_key(__x), _VSTD::move(__x));
     }
 
-    template <class _Pp, class = typename enable_if<
-            !__is_same_uncvref<_Pp, __container_value_type>::value
-        >::type>
+    template <class _Pp, class = __enable_if_t<!__is_same_uncvref<_Pp, __container_value_type>::value> >
     _LIBCPP_INLINE_VISIBILITY
     pair<iterator, bool> __insert_unique(_Pp&& __x) {
       return __emplace_unique(_VSTD::forward<_Pp>(__x));
diff --git a/libcxx/include/__mutex_base b/libcxx/include/__mutex_base
index da056b6d1423..ac0d090b7d19 100644
--- a/libcxx/include/__mutex_base
+++ b/libcxx/include/__mutex_base
@@ -338,11 +338,7 @@ private:
 
 template <class _Rep, class _Period>
 inline _LIBCPP_INLINE_VISIBILITY
-typename enable_if
-<
-    is_floating_point<_Rep>::value,
-    chrono::nanoseconds
->::type
+__enable_if_t<is_floating_point<_Rep>::value, chrono::nanoseconds>
 __safe_nanosecond_cast(chrono::duration<_Rep, _Period> __d)
 {
     using namespace chrono;
@@ -365,11 +361,7 @@ __safe_nanosecond_cast(chrono::duration<_Rep, _Period> __d)
 
 template <class _Rep, class _Period>
 inline _LIBCPP_INLINE_VISIBILITY
-typename enable_if
-<
-    !is_floating_point<_Rep>::value,
-    chrono::nanoseconds
->::type
+__enable_if_t<!is_floating_point<_Rep>::value, chrono::nanoseconds>
 __safe_nanosecond_cast(chrono::duration<_Rep, _Period> __d)
 {
     using namespace chrono;
diff --git a/libcxx/include/__split_buffer b/libcxx/include/__split_buffer
index e484e70440c9..c1c03dd741b0 100644
--- a/libcxx/include/__split_buffer
+++ b/libcxx/include/__split_buffer
@@ -118,19 +118,10 @@ public:
     void __construct_at_end(size_type __n);
     void __construct_at_end(size_type __n, const_reference __x);
     template <class _InputIter>
-        typename enable_if
-        <
-            __is_cpp17_input_iterator<_InputIter>::value &&
-           !__is_cpp17_forward_iterator<_InputIter>::value,
-            void
-        >::type
+    __enable_if_t<__is_cpp17_input_iterator<_InputIter>::value && !__is_cpp17_forward_iterator<_InputIter>::value>
         __construct_at_end(_InputIter __first, _InputIter __last);
     template <class _ForwardIterator>
-        typename enable_if
-        <
-            __is_cpp17_forward_iterator<_ForwardIterator>::value,
-            void
-        >::type
+    __enable_if_t<__is_cpp17_forward_iterator<_ForwardIterator>::value>
         __construct_at_end(_ForwardIterator __first, _ForwardIterator __last);
 
     _LIBCPP_INLINE_VISIBILITY void __destruct_at_begin(pointer __new_begin)
@@ -239,12 +230,7 @@ __split_buffer<_Tp, _Allocator>::__construct_at_end(size_type __n, const_referen
 
 template <class _Tp, class _Allocator>
 template <class _InputIter>
-typename enable_if
-<
-     __is_cpp17_input_iterator<_InputIter>::value &&
-    !__is_cpp17_forward_iterator<_InputIter>::value,
-    void
->::type
+__enable_if_t<__is_cpp17_input_iterator<_InputIter>::value && !__is_cpp17_forward_iterator<_InputIter>::value>
 __split_buffer<_Tp, _Allocator>::__construct_at_end(_InputIter __first, _InputIter __last)
 {
     __alloc_rr& __a = this->__alloc();
@@ -267,11 +253,7 @@ __split_buffer<_Tp, _Allocator>::__construct_at_end(_InputIter __first, _InputIt
 
 template <class _Tp, class _Allocator>
 template <class _ForwardIterator>
-typename enable_if
-<
-    __is_cpp17_forward_iterator<_ForwardIterator>::value,
-    void
->::type
+__enable_if_t<__is_cpp17_forward_iterator<_ForwardIterator>::value>
 __split_buffer<_Tp, _Allocator>::__construct_at_end(_ForwardIterator __first, _ForwardIterator __last)
 {
     _ConstructTransaction __tx(&this->__end_, _VSTD::distance(__first, __last));
diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index e5dd1f4d45ea..8d8449706871 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -597,8 +597,7 @@ struct __tree_key_value_types<__value_type<_Key, _Tp> > {
 
   template <class _Up>
   _LIBCPP_INLINE_VISIBILITY
-  static typename enable_if<__is_same_uncvref<_Up, __container_value_type>::value,
-      key_type const&>::type
+  static __enable_if_t<__is_same_uncvref<_Up, __container_value_type>::value, key_type const&>
   __get_key(_Up& __t) {
     return __t.first;
   }
@@ -611,8 +610,7 @@ struct __tree_key_value_types<__value_type<_Key, _Tp> > {
 
   template <class _Up>
   _LIBCPP_INLINE_VISIBILITY
-  static typename enable_if<__is_same_uncvref<_Up, __container_value_type>::value,
-      __container_value_type const&>::type
+  static __enable_if_t<__is_same_uncvref<_Up, __container_value_type>::value, __container_value_type const&>
   __get_value(_Up& __t) {
     return __t;
   }
@@ -1175,10 +1173,8 @@ public:
 
     template <class _First, class _Second>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<
-        __can_extract_map_key<_First, key_type, __container_value_type>::value,
-        pair<iterator, bool>
-    >::type __emplace_unique(_First&& __f, _Second&& __s) {
+    __enable_if_t<__can_extract_map_key<_First, key_type, __container_value_type>::value, pair<iterator, bool> >
+    __emplace_unique(_First&& __f, _Second&& __s) {
         return __emplace_unique_key_args(__f, _VSTD::forward<_First>(__f),
                                               _VSTD::forward<_Second>(__s));
     }
@@ -1219,10 +1215,8 @@ public:
 
     template <class _First, class _Second>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<
-        __can_extract_map_key<_First, key_type, __container_value_type>::value,
-        iterator
-    >::type __emplace_hint_unique(const_iterator __p, _First&& __f, _Second&& __s) {
+    __enable_if_t<__can_extract_map_key<_First, key_type, __container_value_type>::value, iterator>
+    __emplace_hint_unique(const_iterator __p, _First&& __f, _Second&& __s) {
         return __emplace_hint_unique_key_args(__p, __f,
                                               _VSTD::forward<_First>(__f),
                                               _VSTD::forward<_Second>(__s)).first;
@@ -1275,21 +1269,15 @@ public:
         return __emplace_hint_unique_key_args(__p, _NodeTypes::__get_key(__v), _VSTD::move(__v)).first;
     }
 
-    template <class _Vp, class = typename enable_if<
-            !is_same<typename __unconstref<_Vp>::type,
-                     __container_value_type
-            >::value
-        >::type>
+    template <class _Vp,
+              class = __enable_if_t<!is_same<typename __unconstref<_Vp>::type, __container_value_type>::value> >
     _LIBCPP_INLINE_VISIBILITY
     pair<iterator, bool> __insert_unique(_Vp&& __v) {
         return __emplace_unique(_VSTD::forward<_Vp>(__v));
     }
 
-    template <class _Vp, class = typename enable_if<
-            !is_same<typename __unconstref<_Vp>::type,
-                     __container_value_type
-            >::value
-        >::type>
+    template <class _Vp,
+              class = __enable_if_t<!is_same<typename __unconstref<_Vp>::type, __container_value_type>::value> >
     _LIBCPP_INLINE_VISIBILITY
     iterator __insert_unique(const_iterator __p, _Vp&& __v) {
         return __emplace_hint_unique(__p, _VSTD::forward<_Vp>(__v));
diff --git a/libcxx/include/__tuple b/libcxx/include/__tuple
index 6d13bb24c579..f85036e7af1d 100644
--- a/libcxx/include/__tuple
+++ b/libcxx/include/__tuple
@@ -30,14 +30,14 @@ using __enable_if_tuple_size_imp = _Tp;
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
     const _Tp,
-    typename enable_if<!is_volatile<_Tp>::value>::type,
+    __enable_if_t<!is_volatile<_Tp>::value>,
     integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
     : public integral_constant<size_t, tuple_size<_Tp>::value> {};
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
     volatile _Tp,
-    typename enable_if<!is_const<_Tp>::value>::type,
+    __enable_if_t<!is_const<_Tp>::value>,
     integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
     : public integral_constant<size_t, tuple_size<_Tp>::value> {};
 
@@ -393,7 +393,7 @@ struct __tuple_sfinae_base {
   template <template <class, class...> class _Trait,
             class ..._LArgs, class ..._RArgs>
   static auto __do_test(__tuple_types<_LArgs...>, __tuple_types<_RArgs...>)
-    -> __all<typename enable_if<_Trait<_LArgs, _RArgs>::value, bool>::type{true}...>;
+    -> __all<__enable_if_t<_Trait<_LArgs, _RArgs>::value, bool>{true}...>;
   template <template <class...> class>
   static auto __do_test(...) -> false_type;
 
diff --git a/libcxx/include/array b/libcxx/include/array
index e96c3d813339..867dd6b1bcc6 100644
--- a/libcxx/include/array
+++ b/libcxx/include/array
@@ -438,12 +438,7 @@ operator>=(const array<_Tp, _Size>& __x, const array<_Tp, _Size>& __y)
 
 template <class _Tp, size_t _Size>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-typename enable_if
-<
-    _Size == 0 ||
-    __is_swappable<_Tp>::value,
-    void
->::type
+__enable_if_t<_Size == 0 || __is_swappable<_Tp>::value, void>
 swap(array<_Tp, _Size>& __x, array<_Tp, _Size>& __y)
                                   _NOEXCEPT_(noexcept(__x.swap(__y)))
 {
diff --git a/libcxx/include/exception b/libcxx/include/exception
index 412e02af3822..955739e49eca 100644
--- a/libcxx/include/exception
+++ b/libcxx/include/exception
@@ -310,7 +310,7 @@ template <class _Ep>
 inline _LIBCPP_INLINE_VISIBILITY
 void
 rethrow_if_nested(const _Ep& __e,
-                  typename enable_if< __can_dynamic_cast<_Ep, nested_exception>::value>::type* = 0)
+                  __enable_if_t< __can_dynamic_cast<_Ep, nested_exception>::value>* = 0)
 {
     const nested_exception* __nep = dynamic_cast<const nested_exception*>(_VSTD::addressof(__e));
     if (__nep)
@@ -321,7 +321,7 @@ template <class _Ep>
 inline _LIBCPP_INLINE_VISIBILITY
 void
 rethrow_if_nested(const _Ep&,
-                  typename enable_if<!__can_dynamic_cast<_Ep, nested_exception>::value>::type* = 0)
+                  __enable_if_t<!__can_dynamic_cast<_Ep, nested_exception>::value>* = 0)
 {
 }
 
diff --git a/libcxx/include/forward_list b/libcxx/include/forward_list
index 6a7272027351..aab3b8715d01 100644
--- a/libcxx/include/forward_list
+++ b/libcxx/include/forward_list
@@ -703,15 +703,11 @@ public:
 
     template <class _InputIterator>
         forward_list(_InputIterator __f, _InputIterator __l,
-                     typename enable_if<
-                       __is_cpp17_input_iterator<_InputIterator>::value
-                     >::type* = nullptr);
+                     __enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value>* = nullptr);
     template <class _InputIterator>
         forward_list(_InputIterator __f, _InputIterator __l,
                      const allocator_type& __a,
-                     typename enable_if<
-                       __is_cpp17_input_iterator<_InputIterator>::value
-                     >::type* = nullptr);
+                     __enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value>* = nullptr);
     forward_list(const forward_list& __x);
     forward_list(const forward_list& __x, const __type_identity_t<allocator_type>& __a);
 
@@ -743,11 +739,7 @@ public:
     // ~forward_list() = default;
 
     template <class _InputIterator>
-        typename enable_if
-        <
-            __is_cpp17_input_iterator<_InputIterator>::value,
-            void
-        >::type
+    __enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value, void>
         assign(_InputIterator __f, _InputIterator __l);
     void assign(size_type __n, const value_type& __v);
 
@@ -823,12 +815,8 @@ public:
     iterator insert_after(const_iterator __p, const value_type& __v);
     iterator insert_after(const_iterator __p, size_type __n, const value_type& __v);
     template <class _InputIterator>
-        _LIBCPP_INLINE_VISIBILITY
-        typename enable_if
-        <
-            __is_cpp17_input_iterator<_InputIterator>::value,
-            iterator
-        >::type
+    _LIBCPP_INLINE_VISIBILITY
+    __enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value, iterator>
         insert_after(const_iterator __p, _InputIterator __f, _InputIterator __l);
 
     iterator erase_after(const_iterator __p);
@@ -977,9 +965,7 @@ forward_list<_Tp, _Alloc>::forward_list(size_type __n, const value_type& __v)
 template <class _Tp, class _Alloc>
 template <class _InputIterator>
 forward_list<_Tp, _Alloc>::forward_list(_InputIterator __f, _InputIterator __l,
-                                        typename enable_if<
-                                          __is_cpp17_input_iterator<_InputIterator>::value
-                                        >::type*)
+                                        __enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value>*)
 {
     insert_after(cbefore_begin(), __f, __l);
 }
@@ -988,9 +974,7 @@ template <class _Tp, class _Alloc>
 template <class _InputIterator>
 forward_list<_Tp, _Alloc>::forward_list(_InputIterator __f, _InputIterator __l,
                                         const allocator_type& __a,
-                                        typename enable_if<
-                                          __is_cpp17_input_iterator<_InputIterator>::value
-                                        >::type*)
+                                        __enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value>*)
     : base(__a)
 {
     insert_after(cbefore_begin(), __f, __l);
@@ -1100,11 +1084,7 @@ forward_list<_Tp, _Alloc>::operator=(initializer_list<value_type> __il)
 
 template <class _Tp, class _Alloc>
 template <class _InputIterator>
-typename enable_if
-<
-    __is_cpp17_input_iterator<_InputIterator>::value,
-    void
->::type
+__enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value, void>
 forward_list<_Tp, _Alloc>::assign(_InputIterator __f, _InputIterator __l)
 {
     iterator __i = before_begin();
@@ -1296,11 +1276,7 @@ forward_list<_Tp, _Alloc>::insert_after(const_iterator __p, size_type __n,
 
 template <class _Tp, class _Alloc>
 template <class _InputIterator>
-typename enable_if
-<
-    __is_cpp17_input_iterator<_InputIterator>::value,
-    typename forward_list<_Tp, _Alloc>::iterator
->::type
+__enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value, typename forward_list<_Tp, _Alloc>::iterator>
 forward_list<_Tp, _Alloc>::insert_after(const_iterator __p,
                                         _InputIterator __f, _InputIterator __l)
 {
diff --git a/libcxx/include/list b/libcxx/include/list
index d75b15c060be..1db29d14b842 100644
--- a/libcxx/include/list
+++ b/libcxx/include/list
@@ -870,10 +870,10 @@ public:
 
     template <class _InpIter>
         list(_InpIter __f, _InpIter __l,
-             typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type* = 0);
+             __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>* = 0);
     template <class _InpIter>
         list(_InpIter __f, _InpIter __l, const allocator_type& __a,
-             typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type* = 0);
+             __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>* = 0);
 
     list(const list& __c);
     list(const list& __c, const __type_identity_t<allocator_type>& __a);
@@ -905,7 +905,7 @@ public:
 
     template <class _InpIter>
         void assign(_InpIter __f, _InpIter __l,
-             typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type* = 0);
+                    __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>* = 0);
     void assign(size_type __n, const value_type& __x);
 
     _LIBCPP_INLINE_VISIBILITY
@@ -1022,7 +1022,7 @@ public:
     iterator insert(const_iterator __p, size_type __n, const value_type& __x);
     template <class _InpIter>
         iterator insert(const_iterator __p, _InpIter __f, _InpIter __l,
-             typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type* = 0);
+                        __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>* = 0);
 
     _LIBCPP_INLINE_VISIBILITY
     void swap(list& __c)
@@ -1220,7 +1220,7 @@ list<_Tp, _Alloc>::list(size_type __n, const value_type& __x)
 template <class _Tp, class _Alloc>
 template <class _InpIter>
 list<_Tp, _Alloc>::list(_InpIter __f, _InpIter __l,
-                        typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type*)
+                        __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>*)
 {
     _VSTD::__debug_db_insert_c(this);
     for (; __f != __l; ++__f)
@@ -1230,7 +1230,7 @@ list<_Tp, _Alloc>::list(_InpIter __f, _InpIter __l,
 template <class _Tp, class _Alloc>
 template <class _InpIter>
 list<_Tp, _Alloc>::list(_InpIter __f, _InpIter __l, const allocator_type& __a,
-                        typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type*)
+                        __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>*)
     : base(__a)
 {
     _VSTD::__debug_db_insert_c(this);
@@ -1355,7 +1355,7 @@ template <class _Tp, class _Alloc>
 template <class _InpIter>
 void
 list<_Tp, _Alloc>::assign(_InpIter __f, _InpIter __l,
-                          typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type*)
+                          __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>*)
 {
     iterator __i = begin();
     iterator __e = end();
@@ -1460,7 +1460,7 @@ template <class _Tp, class _Alloc>
 template <class _InpIter>
 typename list<_Tp, _Alloc>::iterator
 list<_Tp, _Alloc>::insert(const_iterator __p, _InpIter __f, _InpIter __l,
-             typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type*)
+                          __enable_if_t<__is_cpp17_input_iterator<_InpIter>::value>*)
 {
     _LIBCPP_DEBUG_ASSERT(__get_const_db()->__find_c_from_i(_VSTD::addressof(__p)) == this,
                          "list::insert(iterator, range) called with an iterator not referring to this list");
diff --git a/libcxx/include/map b/libcxx/include/map
index 106ed5259ed9..14f9a2773b73 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -792,9 +792,7 @@ public:
     }
 
     template <class _ValueTp,
-              class = typename enable_if<
-                    __is_same_uncvref<_ValueTp, value_type>::value
-                 >::type
+              class = __enable_if_t<__is_same_uncvref<_ValueTp, value_type>::value>
              >
     _LIBCPP_INLINE_VISIBILITY
     __value_type& operator=(_ValueTp&& __v)
@@ -1230,13 +1228,13 @@ public:
     }
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value> >
         _LIBCPP_INLINE_VISIBILITY
         pair<iterator, bool> insert(_Pp&& __p)
             {return __tree_.__insert_unique(_VSTD::forward<_Pp>(__p));}
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value> >
         _LIBCPP_INLINE_VISIBILITY
         iterator insert(const_iterator __pos, _Pp&& __p)
             {return __tree_.__insert_unique(__pos.__i_, _VSTD::forward<_Pp>(__p));}
@@ -1456,11 +1454,11 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, iterator>
     find(const _K2& __k)                           {return __tree_.find(__k);}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,const_iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, const_iterator>
     find(const _K2& __k) const                     {return __tree_.find(__k);}
 #endif
 
@@ -1470,7 +1468,7 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,size_type>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, size_type>
     count(const _K2& __k) const {return __tree_.__count_multi(__k);}
 #endif
 
@@ -1479,7 +1477,7 @@ public:
     bool contains(const key_type& __k) const {return find(__k) != end();}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value, bool>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, bool>
     contains(const _K2& __k) const { return find(__k) != end(); }
 #endif // _LIBCPP_STD_VER > 17
 
@@ -1492,12 +1490,12 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, iterator>
     lower_bound(const _K2& __k)       {return __tree_.lower_bound(__k);}
 
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,const_iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, const_iterator>
     lower_bound(const _K2& __k) const {return __tree_.lower_bound(__k);}
 #endif
 
@@ -1510,11 +1508,11 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, iterator>
     upper_bound(const _K2& __k)       {return __tree_.upper_bound(__k);}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,const_iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, const_iterator>
     upper_bound(const _K2& __k) const {return __tree_.upper_bound(__k);}
 #endif
 
@@ -1527,11 +1525,11 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,pair<iterator,iterator>>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, pair<iterator,iterator>>
     equal_range(const _K2& __k)       {return __tree_.__equal_range_multi(__k);}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,pair<const_iterator,const_iterator>>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, pair<const_iterator,const_iterator>>
     equal_range(const _K2& __k) const {return __tree_.__equal_range_multi(__k);}
 #endif
 
@@ -2000,13 +1998,13 @@ public:
     }
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value>>
         _LIBCPP_INLINE_VISIBILITY
         iterator insert(_Pp&& __p)
             {return __tree_.__insert_multi(_VSTD::forward<_Pp>(__p));}
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value>>
         _LIBCPP_INLINE_VISIBILITY
         iterator insert(const_iterator __pos, _Pp&& __p)
             {return __tree_.__insert_multi(__pos.__i_, _VSTD::forward<_Pp>(__p));}
@@ -2128,11 +2126,11 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, iterator>
     find(const _K2& __k)                           {return __tree_.find(__k);}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,const_iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, const_iterator>
     find(const _K2& __k) const                     {return __tree_.find(__k);}
 #endif
 
@@ -2142,7 +2140,7 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,size_type>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, size_type>
     count(const _K2& __k) const {return __tree_.__count_multi(__k);}
 #endif
 
@@ -2151,7 +2149,7 @@ public:
     bool contains(const key_type& __k) const {return find(__k) != end();}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value, bool>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, bool>
     contains(const _K2& __k) const { return find(__k) != end(); }
 #endif // _LIBCPP_STD_VER > 17
 
@@ -2164,12 +2162,12 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, iterator>
     lower_bound(const _K2& __k)       {return __tree_.lower_bound(__k);}
 
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,const_iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, const_iterator>
     lower_bound(const _K2& __k) const {return __tree_.lower_bound(__k);}
 #endif
 
@@ -2182,11 +2180,11 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, iterator>
     upper_bound(const _K2& __k)       {return __tree_.upper_bound(__k);}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,const_iterator>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, const_iterator>
     upper_bound(const _K2& __k) const {return __tree_.upper_bound(__k);}
 #endif
 
@@ -2199,11 +2197,11 @@ public:
 #if _LIBCPP_STD_VER > 11
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,pair<iterator,iterator>>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, pair<iterator,iterator>>
     equal_range(const _K2& __k)       {return __tree_.__equal_range_multi(__k);}
     template <typename _K2>
     _LIBCPP_INLINE_VISIBILITY
-    typename enable_if<__is_transparent<_Compare, _K2>::value,pair<const_iterator,const_iterator>>::type
+    __enable_if_t<__is_transparent<_Compare, _K2>::value, pair<const_iterator,const_iterator>>
     equal_range(const _K2& __k) const {return __tree_.__equal_range_multi(__k);}
 #endif
 
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 221eb23dd3f8..79527cca5853 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -482,10 +482,7 @@ struct _LIBCPP_DECLSPEC_EMPTY_BASES __tuple_impl<__tuple_indices<_Indx...>, _Tp.
             {}
 
     template <class _Tuple,
-              class = typename enable_if
-                      <
-                         __tuple_constructible<_Tuple, tuple<_Tp...> >::value
-                      >::type
+              class = __enable_if_t<__tuple_constructible<_Tuple, tuple<_Tp...> >::value>
              >
         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
         __tuple_impl(_Tuple&& __t) _NOEXCEPT_((__all<is_nothrow_constructible<_Tp, typename tuple_element<_Indx,
@@ -495,10 +492,7 @@ struct _LIBCPP_DECLSPEC_EMPTY_BASES __tuple_impl<__tuple_indices<_Indx...>, _Tp.
             {}
 
     template <class _Alloc, class _Tuple,
-              class = typename enable_if
-                      <
-                         __tuple_constructible<_Tuple, tuple<_Tp...> >::value
-                      >::type
+              class = __enable_if_t<__tuple_constructible<_Tuple, tuple<_Tp...> >::value>
              >
         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
         __tuple_impl(allocator_arg_t, const _Alloc& __a, _Tuple&& __t)
@@ -1336,11 +1330,7 @@ tuple(allocator_arg_t, _Alloc, tuple<_Tp...>) -> tuple<_Tp...>;
 
 template <class ..._Tp>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-typename enable_if
-<
-    __all<__is_swappable<_Tp>::value...>::value,
-    void
->::type
+__enable_if_t<__all<__is_swappable<_Tp>::value...>::value, void>
 swap(tuple<_Tp...>& __t, tuple<_Tp...>& __u)
                  _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
     {__t.swap(__u);}
diff --git a/libcxx/include/unordered_map b/libcxx/include/unordered_map
index 72749e11e843..7767805f38c6 100644
--- a/libcxx/include/unordered_map
+++ b/libcxx/include/unordered_map
@@ -876,9 +876,7 @@ public:
     }
 
     template <class _ValueTp,
-              class = typename enable_if<
-                    __is_same_uncvref<_ValueTp, value_type>::value
-                 >::type
+              class = __enable_if_t<__is_same_uncvref<_ValueTp, value_type>::value>
              >
     _LIBCPP_INLINE_VISIBILITY
     __hash_value_type& operator=(_ValueTp&& __v)
@@ -1237,13 +1235,13 @@ public:
     }
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value> >
         _LIBCPP_INLINE_VISIBILITY
         pair<iterator, bool> insert(_Pp&& __x)
             {return __table_.__insert_unique(_VSTD::forward<_Pp>(__x));}
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value> >
         _LIBCPP_INLINE_VISIBILITY
         iterator insert(const_iterator __p, _Pp&& __x)
         {
@@ -2114,13 +2112,13 @@ public:
         {return __table_.__insert_multi(__p.__i_, _VSTD::move(__x));}
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value> >
     _LIBCPP_INLINE_VISIBILITY
     iterator insert(_Pp&& __x)
         {return __table_.__insert_multi(_VSTD::forward<_Pp>(__x));}
 
     template <class _Pp,
-              class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
+              class = __enable_if_t<is_constructible<value_type, _Pp>::value> >
     _LIBCPP_INLINE_VISIBILITY
     iterator insert(const_iterator __p, _Pp&& __x)
         {return __table_.__insert_multi(__p.__i_, _VSTD::forward<_Pp>(__x));}