Patchwork [v3] Another try at LWG 2141

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Submitter Paolo Carlini
Date Oct. 24, 2012, 8:40 p.m.
Message ID <50885221.1030803@oracle.com>
Download mbox | patch
Permalink /patch/193949/
State New
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Comments

Paolo Carlini - Oct. 24, 2012, 8:40 p.m.
Hi,

let's try again ;) In the light of discussion in Portland, which liked 
Marc's idea of using std::decay in the unary common_type too, the below 
seems good to go now, given that there are bad interactions with the 
front-end bug we have got.

Tested x86_64-linux.

Thanks,
Paolo.

///////////////////////
2012-10-24  Daniel Krugler  <daniel.kruegler@gmail.com>

	* include/std/type_traits (common_type): Implement LWG 2141.
	* testsuite/20_util/duration/requirements/sfinae_friendly_1.cc:
	Update.
	* testsuite/20_util/common_type/requirements/typedefs-1.cc: Likewise.
	* testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc:
	Likewise.
	* testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc:
	Likewise.
	* testsuite/20_util/common_type/requirements/typedefs-2.cc: Likewise.
Marc Glisse - Oct. 24, 2012, 8:52 p.m.
On Wed, 24 Oct 2012, Paolo Carlini wrote:

> let's try again ;) In the light of discussion in Portland, which liked Marc's 
> idea of using std::decay in the unary common_type too, the below seems good 
> to go now, given that there are bad interactions with the front-end bug we 
> have got.

    template<typename _Tp>
      struct common_type<_Tp>
-    { typedef _Tp type; };
+    { typedef typename decay<_Tp>::type type; };

(talking to myself)
I guess decay never has sfinae-type errors, so it doesn't matter whether 
we have this typedef or derive from decay.
Daniel Kr├╝gler - Oct. 24, 2012, 8:58 p.m.
2012/10/24 Marc Glisse <marc.glisse@inria.fr>:
> On Wed, 24 Oct 2012, Paolo Carlini wrote:
>
>> let's try again ;) In the light of discussion in Portland, which liked
>> Marc's idea of using std::decay in the unary common_type too, the below
>> seems good to go now, given that there are bad interactions with the
>> front-end bug we have got.
>
>
>    template<typename _Tp>
>      struct common_type<_Tp>
> -    { typedef _Tp type; };
> +    { typedef typename decay<_Tp>::type type; };
>
> (talking to myself)
> I guess decay never has sfinae-type errors, so it doesn't matter whether we
> have this typedef or derive from decay.

Depending on the final resolution of

http://cplusplus.github.com/LWG/lwg-active.html#2101

(the worst IMO) std::decay could produce an invalid instantiation, a
less aggressive
variant would make this sfinae-friendly (not type), but hopefully it
will always be well-formed.
I'm awaiting the further development of that issue.

- Daniel

Patch

Index: include/std/type_traits
===================================================================
--- include/std/type_traits	(revision 192762)
+++ include/std/type_traits	(working copy)
@@ -1792,9 +1792,9 @@ 
   struct __do_common_type_impl
   {
     template<typename _Tp, typename _Up>
-      static __success_type<decltype
+      static __success_type<typename decay<decltype
 			    (true ? std::declval<_Tp>()
-			     : std::declval<_Up>())> _S_test(int);
+			     : std::declval<_Up>())>::type> _S_test(int);
 
     template<typename, typename>
       static __failure_type _S_test(...);
@@ -1835,7 +1835,7 @@ 
 
   template<typename _Tp>
     struct common_type<_Tp>
-    { typedef _Tp type; };
+    { typedef typename decay<_Tp>::type type; };
 
   template<typename _Tp, typename _Up>
     struct common_type<_Tp, _Up>
Index: testsuite/20_util/duration/requirements/sfinae_friendly_1.cc
===================================================================
--- testsuite/20_util/duration/requirements/sfinae_friendly_1.cc	(revision 192762)
+++ testsuite/20_util/duration/requirements/sfinae_friendly_1.cc	(working copy)
@@ -21,9 +21,6 @@ 
 #include <type_traits>
 #include <chrono>
 
-//TODO: Uncomment this once gcc bug 53000 has been resolved:
-//#define HAS_53000_FIXED
-
 // Helper types:
 struct has_type_impl
 {
@@ -55,10 +52,8 @@ 
 typedef std::chrono::duration<double, std::nano> ddn;
 typedef std::chrono::duration<int, std::milli> dim;
 
-#ifdef HAS_53000_FIXED
-static_assert(is_type<std::common_type<din, din>, din&&>(), "");
-static_assert(is_type<std::common_type<din, din, din>, din&&>(), "");
-#endif
+static_assert(is_type<std::common_type<din, din>, din>(), "");
+static_assert(is_type<std::common_type<din, din, din>, din>(), "");
 
 static_assert(is_type<std::common_type<din, ddn>, ddn>(), "");
 static_assert(is_type<std::common_type<din, din, ddn>, ddn>(), "");
Index: testsuite/20_util/common_type/requirements/typedefs-1.cc
===================================================================
--- testsuite/20_util/common_type/requirements/typedefs-1.cc	(revision 192762)
+++ testsuite/20_util/common_type/requirements/typedefs-1.cc	(working copy)
@@ -105,7 +105,7 @@ 
   COMMON_TYPE_TEST_ALL_2(int, int, int, 1);
   COMMON_TYPE_TEST_ALL_2(int, double, double, 2);
   COMMON_TYPE_TEST_2(NO_CV, A, A, A, 3);
-  COMMON_TYPE_TEST_2(const, A, A, const A, 4);
+  COMMON_TYPE_TEST_2(const, A, A, A, 4);
   COMMON_TYPE_TEST_2(NO_CV, B, A, A, 5);  
 }
 
Index: testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc
===================================================================
--- testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc	(revision 192762)
+++ testsuite/20_util/common_type/requirements/sfinae_friendly_1.cc	(working copy)
@@ -163,23 +163,19 @@ 
   };
 }
 
-#ifdef HAS_53000_FIXED
-static_assert(is_type<std::common_type<int, int>, int&&>(), "");
-static_assert(is_type<std::common_type<ScEn, ScEn>, ScEn&&>(), "");
-static_assert(is_type<std::common_type<UnscEn, UnscEn>, UnscEn&&>(), "");
-#endif
+static_assert(is_type<std::common_type<int, int>, int>(), "");
+static_assert(is_type<std::common_type<ScEn, ScEn>, ScEn>(), "");
+static_assert(is_type<std::common_type<UnscEn, UnscEn>, UnscEn>(), "");
 static_assert(is_type<std::common_type<UnscEn, int>, int>(), "");
-#ifdef HAS_53000_FIXED
-static_assert(is_type<std::common_type<int, int, int>, int&&>(), "");
-static_assert(is_type<std::common_type<int, int, int, int>, int&&>(), "");
-static_assert(is_type<std::common_type<int, int, int, int, int>, int&&>(), "");
-static_assert(is_type<std::common_type<S, S>, S&&>(), "");
-static_assert(is_type<std::common_type<const S, const S>, const S&&>(), "");
+static_assert(is_type<std::common_type<int, int, int>, int>(), "");
+static_assert(is_type<std::common_type<int, int, int, int>, int>(), "");
+static_assert(is_type<std::common_type<int, int, int, int, int>, int>(), "");
+static_assert(is_type<std::common_type<S, S>, S>(), "");
+static_assert(is_type<std::common_type<const S, const S>, S>(), "");
 static_assert(is_type<std::common_type<std::initializer_list<int>,
-	      std::initializer_list<int>>, std::initializer_list<int>&&>(), "");
-static_assert(is_type<std::common_type<B, D>, B&&>(), "");
-static_assert(is_type<std::common_type<D, B>, B&&>(), "");
-#endif
+	      std::initializer_list<int>>, std::initializer_list<int>>(), "");
+static_assert(is_type<std::common_type<B, D>, B>(), "");
+static_assert(is_type<std::common_type<D, B>, B>(), "");
 static_assert(is_type<std::common_type<F1, F2>, void*>(), "");
 static_assert(is_type<std::common_type<F2, F1>, void*>(), "");
 static_assert(is_type<std::common_type<G1, G2>, const volatile void*>(), "");
@@ -191,16 +187,12 @@ 
 static_assert(is_type<std::common_type<void, void>, void>(), "");
 static_assert(is_type<std::common_type<const void, const void>, void>(), "");
 static_assert(is_type<std::common_type<int&, int&&>, int>(), "");
-static_assert(is_type<std::common_type<int&, int&>, int&>(), "");
-#ifdef HAS_53000_FIXED
-static_assert(is_type<std::common_type<int&&, int&&>, int&&>(), "");
-static_assert(is_type<std::common_type<int&&, const int&&>, const int&&>(), "");
-#endif
-static_assert(is_type<std::common_type<U&, const U&&>, const U>(), "");
-static_assert(is_type<std::common_type<U&, U&>, U&>(), "");
-#ifdef HAS_53000_FIXED
-static_assert(is_type<std::common_type<U&&, U&&>, U&&>(), "");
-#endif
+static_assert(is_type<std::common_type<int&, int&>, int>(), "");
+static_assert(is_type<std::common_type<int&&, int&&>, int>(), "");
+static_assert(is_type<std::common_type<int&&, const int&&>, int>(), "");
+static_assert(is_type<std::common_type<U&, const U&&>, U>(), "");
+static_assert(is_type<std::common_type<U&, U&>, U>(), "");
+static_assert(is_type<std::common_type<U&&, U&&>, U>(), "");
 static_assert(is_type<std::common_type<int B::*, int D::*>, int D::*>(), "");
 static_assert(is_type<std::common_type<int D::*, int B::*>, int D::*>(), "");
 static_assert(is_type<std::common_type<const int B::*, volatile int D::*>,
@@ -209,34 +201,28 @@ 
 	      int (D::*)()>(), "");
 static_assert(is_type<std::common_type<int (B::*)() const, int (D::*)() const>,
 	      int (D::*)() const>(), "");
-#ifdef HAS_53000_FIXED
-static_assert(is_type<std::common_type<int[3], int[3]>, int(&&)[3]>(), "");
-#endif
+static_assert(is_type<std::common_type<int[3], int[3]>, int*>(), "");
 static_assert(is_type<std::common_type<int[1], const int[3]>,
 	      const int*>(), "");
-static_assert(is_type<std::common_type<void(), void()>, void(&)()>(), "");
-static_assert(is_type<std::common_type<void(&)(), void(&)()>, void(&)()>(), "");
+static_assert(is_type<std::common_type<void(), void()>, void(*)()>(), "");
+static_assert(is_type<std::common_type<void(&)(), void(&)()>, void(*)()>(), "");
 static_assert(is_type<std::common_type<void(&)(), void(&&)()>,
-	      void(&)()>(), "");
+	      void(*)()>(), "");
 static_assert(is_type<std::common_type<void(&&)(), void(&)()>,
-	      void(&)()>(), "");
+	      void(*)()>(), "");
 static_assert(is_type<std::common_type<void(&&)(), void(&&)()>,
-	      void(&)()>(), "");
+	      void(*)()>(), "");
 static_assert(is_type<std::common_type<ImplicitTo<int>, int>, int>(), "");
-#ifdef HAS_53000_FIXED
 static_assert(is_type<std::common_type<ImplicitTo<int>, ImplicitTo<int>>,
-	      ImplicitTo<int>&&>(), "");
-#endif
+	      ImplicitTo<int>>(), "");
 static_assert(is_type<std::common_type<ImplicitTo<int>, int,
 	      ImplicitTo<int>>, int>(), "");
-#ifdef HAS_53000_FIXED
 static_assert(is_type<std::common_type<ExplicitTo<int>, ExplicitTo<int>>,
-	      ExplicitTo<int>&&>(), "");
+	      ExplicitTo<int>>(), "");
 static_assert(is_type<std::common_type<decltype(lmd1), decltype(lmd1)>,
-	      decltype(lmd1)&&>(), "");
-#endif
+	      decltype(lmd1)>(), "");
 static_assert(is_type<std::common_type<decltype(lmd1)&, decltype(lmd1)&>,
-	      decltype(lmd1)&>(), "");
+	      decltype(lmd1)>(), "");
 static_assert(is_type<std::common_type<decltype(lmd1)&, decltype(lmd2)&>,
 	      void(*)(int, double)>(), "");
 static_assert(is_type<std::common_type<decltype(nullptr), void*>, void*>(), "");
@@ -251,9 +237,9 @@ 
 	      int (B::*)() const>(), "");
 static_assert(is_type<std::common_type<decltype(nullptr), const int B::*>,
 	      const int B::*>(), "");
-static_assert(is_type<std::common_type<Abstract&, Abstract&>, Abstract&>(), "");
-static_assert(is_type<std::common_type<Ukn&, Ukn&>, Ukn&>(), "");
-static_assert(is_type<std::common_type<ImplicitTo<B&>, B&>, B&>(), "");
+static_assert(is_type<std::common_type<Abstract&, Abstract&>, Abstract>(), "");
+static_assert(is_type<std::common_type<Ukn&, Ukn&>, Ukn>(), "");
+static_assert(is_type<std::common_type<ImplicitTo<B&>, B&>, B>(), "");
 static_assert(is_type<std::common_type<ImplicitTo<B&>&, B&&>, B>(), "");
 static_assert(is_type<std::common_type<UConv1, const Abstract*&>,
 	      const Abstract*>(), "");
@@ -262,12 +248,12 @@ 
 
 #ifdef HAS_53000_FIXED
 static_assert(is_type<std::common_type<Abstract&&, Abstract&&>,
-	      Abstract&&>(), "");
+	      Abstract>(), "");
 static_assert(is_type<std::common_type<const Abstract&&,
-				       volatile Abstract&&>, const volatile Abstract&&>(), "");
-static_assert(is_type<std::common_type<Ukn&&, Ukn&&>, Ukn&&>(), "");
+				       volatile Abstract&&>, Abstract>(), "");
+static_assert(is_type<std::common_type<Ukn&&, Ukn&&>, Ukn>(), "");
 static_assert(is_type<std::common_type<const Ukn&&, volatile Ukn&&>,
-	      const volatile Ukn&&>(), "");
+	      Ukn>(), "");
 #endif
 
 static_assert(is_type<std::common_type<X1, X2>, RX12>(), "");
@@ -337,14 +323,12 @@ 
   auto local_lmd1 = [=](int, double) { return i + i; };
   auto local_lmd2 = [=](int, double) { return i - i; };
 
-#ifdef HAS_53000_FIXED
   static_assert(is_type<std::common_type<decltype(local_lmd1),
-		        decltype(local_lmd1)>, decltype(local_lmd1)&&>(), "");
-#endif
+		        decltype(local_lmd1)>, decltype(local_lmd1)>(), "");
   static_assert(is_type<std::common_type<decltype(local_lmd1)&,
 		        decltype(local_lmd1)>, decltype(local_lmd1)>(), "");
   static_assert(is_type<std::common_type<decltype(local_lmd1)&,
-			decltype(local_lmd1)&>, decltype(local_lmd1)&>(), "");
+			decltype(local_lmd1)&>, decltype(local_lmd1)>(), "");
 
   static_assert(!has_type<std::common_type<decltype(local_lmd1),
 		decltype(lmd1)>>(), "");
Index: testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc
===================================================================
--- testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc	(revision 192762)
+++ testsuite/20_util/common_type/requirements/sfinae_friendly_2.cc	(working copy)
@@ -24,12 +24,11 @@ 
 
 template<typename... Args>
 constexpr
-std::array<typename std::decay<typename std::common_type<Args...>::type>::type, 
+std::array<typename std::common_type<Args...>::type, 
   sizeof...(Args)>
 make_array(Args&&... args)  // { dg-error "invalid use" }
 {
-  typedef typename std::decay<typename std::common_type<Args...>::type>::type 
-    CT;
+  typedef typename std::common_type<Args...>::type CT;
   return std::array<CT, sizeof...(Args)>{static_cast<CT>
       (std::forward<Args>(args))...};
 }
@@ -39,10 +38,26 @@ 
   constexpr auto a1 = make_array(0);
   constexpr auto a2 = make_array(0, 1.2);
   constexpr auto a3 = make_array(5, true, 3.1415f, 'c');
+  
+  int i{};
+  double d{1.2};
+  float f{3.1415f};
+  
+  auto b1 = make_array(i);
+  auto b2 = make_array(i, 1.2);
+  auto b3 = make_array(i, d);
+  auto b4 = make_array(0, d);
+  auto b5 = make_array(i, true, f, 'c');
 
   static_assert(std::is_same<decltype(a1), const std::array<int, 1>>(), "");
   static_assert(std::is_same<decltype(a2), const std::array<double, 2>>(), "");
   static_assert(std::is_same<decltype(a3), const std::array<float, 4>>(), "");
+
+  static_assert(std::is_same<decltype(b1), std::array<int, 1>>(), "");
+  static_assert(std::is_same<decltype(b2), std::array<double, 2>>(), "");
+  static_assert(std::is_same<decltype(b3), std::array<double, 2>>(), "");
+  static_assert(std::is_same<decltype(b4), std::array<double, 2>>(), "");
+  static_assert(std::is_same<decltype(b5), std::array<float, 4>>(), "");
 }
 
 void test02()
Index: testsuite/20_util/common_type/requirements/typedefs-2.cc
===================================================================
--- testsuite/20_util/common_type/requirements/typedefs-2.cc	(revision 192762)
+++ testsuite/20_util/common_type/requirements/typedefs-2.cc	(working copy)
@@ -1,7 +1,7 @@ 
 // { dg-options "-std=gnu++0x" }
 // 2009-11-12  Paolo Carlini  <paolo.carlini@oracle.com>
 //
-// Copyright (C) 2009 Free Software Foundation, Inc.
+// Copyright (C) 2009-2012 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -29,10 +29,9 @@ 
   using std::is_same;
 
   VERIFY( (is_same<common_type<void>::type, void>::value) );
-  VERIFY( (is_same<common_type<const void>::type, const void>::value) );
-  VERIFY( (is_same<common_type<volatile void>::type, volatile void>::value) );
-  VERIFY( (is_same<common_type<const volatile void>::type,
-	           const volatile void>::value) );
+  VERIFY( (is_same<common_type<const void>::type, void>::value) );
+  VERIFY( (is_same<common_type<volatile void>::type, void>::value) );
+  VERIFY( (is_same<common_type<const volatile void>::type, void>::value) );
 
   VERIFY( (is_same<common_type<void, void>::type, void>::value) );
   VERIFY( (is_same<common_type<void, const void>::type, void>::value) );