Attempt to work around C++20 operator rewriting causinginfinite recursion.

Fixes https://github.com/boostorg/utility/issues/65.

.travis.yml

@@ -136,6 +136,17 @@ matrix:
           sources:
             - sourceline: "ppa:ubuntu-toolchain-r/test"
 
+    - os: linux
+      dist: bionic
+      compiler: gcc-10
+      env: TOOLSET=gcc COMPILER=g++-10 CXXSTD=03,11,14,17,20
+      addons:
+        apt:
+          packages:
+            - g++-10
+          sources:
+            - sourceline: "ppa:ubuntu-toolchain-r/test"
+
 # clang, Linux
     - os: linux
       dist: trusty
@@ -293,17 +304,31 @@ matrix:
 
     - os: linux
       dist: xenial
-      compiler: clang-libc++
-      env: TOOLSET=clang COMPILER=clang++-9 CXXSTD=03,11,14,17,2a CXXFLAGS="-stdlib=libc++" LINKFLAGS="-stdlib=libc++"
+      compiler: clang-10
+      env: TOOLSET=clang COMPILER=clang++-10 CXXSTD=03,11,14,17,20
       addons:
         apt:
           packages:
-            - clang-9
-            - libc++-9-dev
-            - libc++abi-9-dev
+            - clang-10
+            - libstdc++-9-dev
           sources:
             - sourceline: "ppa:ubuntu-toolchain-r/test"
-            - sourceline: "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main"
+            - sourceline: "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-10 main"
+              key_url: "https://apt.llvm.org/llvm-snapshot.gpg.key"
+
+    - os: linux
+      dist: xenial
+      compiler: clang-libc++
+      env: TOOLSET=clang COMPILER=clang++-10 CXXSTD=03,11,14,17,20 CXXFLAGS="-stdlib=libc++" LINKFLAGS="-stdlib=libc++"
+      addons:
+        apt:
+          packages:
+            - clang-10
+            - libc++-10-dev
+            - libc++abi-10-dev
+          sources:
+            - sourceline: "ppa:ubuntu-toolchain-r/test"
+            - sourceline: "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-10 main"
               key_url: "https://apt.llvm.org/llvm-snapshot.gpg.key"
 
 # clang, OS X

CMakeLists.txt

@@ -20,6 +20,7 @@ target_link_libraries(boost_utility
         Boost::config
         Boost::container_hash
         Boost::core
+        Boost::io
         Boost::preprocessor
         Boost::static_assert
         Boost::throw_exception

appveyor.yml

@@ -15,9 +15,10 @@ branches:
 
 environment:
   matrix:
-    - TOOLSET: msvc-9.0,msvc-10.0,msvc-11.0,msvc-12.0
+    - TOOLSET: msvc-9.0,msvc-10.0,msvc-11.0
+      ADDRMD: 32
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-    - TOOLSET: msvc-14.0
+    - TOOLSET: msvc-12.0,msvc-14.0
       ADDRMD: 32,64
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
     - TOOLSET: msvc-14.1

doc/declval.qbk

@@ -1,6 +1,6 @@
 [/
  / Copyright (c) 2008 Howard Hinnant
- / Copyright (c) 2009-20012 Vicente J. Botet Escriba
+ / Copyright (c) 2009-2012 Vicente J. Botet Escriba
  /
  / Distributed under the Boost Software License, Version 1.0. (See accompanying
  / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

include/boost/detail/call_traits.hpp

@@ -100,7 +100,7 @@ struct call_traits<T&>
    typedef T& param_type;  // hh removed const
 };
 
-#if BOOST_WORKAROUND( __BORLANDC__,  < 0x5A0 )
+#if BOOST_WORKAROUND( BOOST_BORLANDC,  < 0x5A0 )
 // these are illegal specialisations; cv-qualifies applied to
 // references have no effect according to [8.3.2p1],
 // C++ Builder requires them though as it treats cv-qualified

include/boost/operators.hpp

@@ -100,6 +100,11 @@
 #include <boost/config.hpp>
 #include <boost/detail/workaround.hpp>
 #include <boost/core/addressof.hpp>
+#if defined(__cpp_impl_three_way_comparison)
+#include <boost/core/enable_if.hpp>
+#include <boost/type_traits/is_same.hpp>
+#include <boost/type_traits/declval.hpp>
+#endif
 
 #if defined(__sgi) && !defined(__GNUC__)
 #   pragma set woff 1234
@@ -109,6 +114,13 @@
 #   pragma warning( disable : 4284 ) // complaint about return type of
 #endif                               // operator-> not begin a UDT
 
+// Define BOOST_OPERATORS_CONSTEXPR to be like BOOST_CONSTEXPR but empty under MSVC < v19.22
+#if BOOST_WORKAROUND(BOOST_MSVC, < 1922)
+#define BOOST_OPERATORS_CONSTEXPR
+#else
+#define BOOST_OPERATORS_CONSTEXPR BOOST_CONSTEXPR
+#endif
+
 // In this section we supply the xxxx1 and xxxx2 forms of the operator
 // templates, which are explicitly targeted at the 1-type-argument and
 // 2-type-argument operator forms, respectively.
@@ -132,34 +144,46 @@ template <typename T> class empty_base {};
 template <class T, class U, class B = operators_detail::empty_base<T> >
 struct less_than_comparable2 : B
 {
-     friend bool operator<=(const T& x, const U& y) { return !static_cast<bool>(x > y); }
-     friend bool operator>=(const T& x, const U& y) { return !static_cast<bool>(x < y); }
-     friend bool operator>(const U& x, const T& y)  { return y < x; }
-     friend bool operator<(const U& x, const T& y)  { return y > x; }
-     friend bool operator<=(const U& x, const T& y) { return !static_cast<bool>(y < x); }
-     friend bool operator>=(const U& x, const T& y) { return !static_cast<bool>(y > x); }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator<=(const T& x, const U& y) { return !static_cast<bool>(x > y); }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator>=(const T& x, const U& y) { return !static_cast<bool>(x < y); }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator>(const U& x, const T& y)  { return y < x; }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator<(const U& x, const T& y)  { return y > x; }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator<=(const U& x, const T& y) { return !static_cast<bool>(y < x); }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator>=(const U& x, const T& y) { return !static_cast<bool>(y > x); }
 };
 
 template <class T, class B = operators_detail::empty_base<T> >
 struct less_than_comparable1 : B
 {
-     friend bool operator>(const T& x, const T& y)  { return y < x; }
-     friend bool operator<=(const T& x, const T& y) { return !static_cast<bool>(y < x); }
-     friend bool operator>=(const T& x, const T& y) { return !static_cast<bool>(x < y); }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator>(const T& x, const T& y)  { return y < x; }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator<=(const T& x, const T& y) { return !static_cast<bool>(y < x); }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator>=(const T& x, const T& y) { return !static_cast<bool>(x < y); }
 };
 
 template <class T, class U, class B = operators_detail::empty_base<T> >
 struct equality_comparable2 : B
 {
-     friend bool operator==(const U& y, const T& x) { return x == y; }
-     friend bool operator!=(const U& y, const T& x) { return !static_cast<bool>(x == y); }
-     friend bool operator!=(const T& y, const U& x) { return !static_cast<bool>(y == x); }
+#if defined(__cpp_impl_three_way_comparison)
+     template< typename R = decltype(boost::declval< T const& >() == boost::declval< U const& >()) >
+     friend BOOST_OPERATORS_CONSTEXPR
+     typename boost::enable_if_c< !boost::is_same< R, bool >::value, bool >::type
+     operator==(const U& y, const T& x) { return x == y; }
+
+     template< typename R = decltype(boost::declval< T const& >() == boost::declval< U const& >()) >
+     friend BOOST_OPERATORS_CONSTEXPR
+     typename boost::enable_if_c< !boost::is_same< R, bool >::value, bool >::type
+     operator!=(const U& y, const T& x) { return !static_cast<bool>(x == y); }
+#else
+     friend BOOST_OPERATORS_CONSTEXPR bool operator==(const U& y, const T& x) { return x == y; }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator!=(const U& y, const T& x) { return !static_cast<bool>(x == y); }
+#endif
+     friend BOOST_OPERATORS_CONSTEXPR bool operator!=(const T& x, const U& y) { return !static_cast<bool>(x == y); }
 };
 
 template <class T, class B = operators_detail::empty_base<T> >
 struct equality_comparable1 : B
 {
-     friend bool operator!=(const T& x, const T& y) { return !static_cast<bool>(x == y); }
+     friend BOOST_OPERATORS_CONSTEXPR bool operator!=(const T& x, const T& y) { return !static_cast<bool>(x == y); }
 };
 
 // A macro which produces "name_2left" from "name".
@@ -362,7 +386,7 @@ BOOST_BINARY_OPERATOR( right_shiftable, >> )
 template <class T, class U, class B = operators_detail::empty_base<T> >
 struct equivalent2 : B
 {
-  friend bool operator==(const T& x, const U& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator==(const T& x, const U& y)
   {
     return !static_cast<bool>(x < y) && !static_cast<bool>(x > y);
   }
@@ -371,7 +395,7 @@ struct equivalent2 : B
 template <class T, class B = operators_detail::empty_base<T> >
 struct equivalent1 : B
 {
-  friend bool operator==(const T&x, const T&y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator==(const T&x, const T&y)
   {
     return !static_cast<bool>(x < y) && !static_cast<bool>(y < x);
   }
@@ -380,28 +404,28 @@ struct equivalent1 : B
 template <class T, class U, class B = operators_detail::empty_base<T> >
 struct partially_ordered2 : B
 {
-  friend bool operator<=(const T& x, const U& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator<=(const T& x, const U& y)
     { return static_cast<bool>(x < y) || static_cast<bool>(x == y); }
-  friend bool operator>=(const T& x, const U& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator>=(const T& x, const U& y)
     { return static_cast<bool>(x > y) || static_cast<bool>(x == y); }
-  friend bool operator>(const U& x, const T& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator>(const U& x, const T& y)
     { return y < x; }
-  friend bool operator<(const U& x, const T& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator<(const U& x, const T& y)
     { return y > x; }
-  friend bool operator<=(const U& x, const T& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator<=(const U& x, const T& y)
     { return static_cast<bool>(y > x) || static_cast<bool>(y == x); }
-  friend bool operator>=(const U& x, const T& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator>=(const U& x, const T& y)
     { return static_cast<bool>(y < x) || static_cast<bool>(y == x); }
 };
 
 template <class T, class B = operators_detail::empty_base<T> >
 struct partially_ordered1 : B
 {
-  friend bool operator>(const T& x, const T& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator>(const T& x, const T& y)
     { return y < x; }
-  friend bool operator<=(const T& x, const T& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator<=(const T& x, const T& y)
     { return static_cast<bool>(x < y) || static_cast<bool>(x == y); }
-  friend bool operator>=(const T& x, const T& y)
+  friend BOOST_OPERATORS_CONSTEXPR bool operator>=(const T& x, const T& y)
     { return static_cast<bool>(y < x) || static_cast<bool>(x == y); }
 };
 

include/boost/operators_v1.hpp

@@ -144,9 +144,11 @@ struct less_than_comparable1 : B
 template <class T, class U, class B = ::boost::detail::empty_base<T> >
 struct equality_comparable2 : B
 {
+#if !defined(__cpp_impl_three_way_comparison)
      friend bool operator==(const U& y, const T& x) { return x == y; }
      friend bool operator!=(const U& y, const T& x) { return !static_cast<bool>(x == y); }
-     friend bool operator!=(const T& y, const U& x) { return !static_cast<bool>(y == x); }
+#endif
+     friend bool operator!=(const T& x, const U& y) { return !static_cast<bool>(x == y); }
 };
 
 template <class T, class B = ::boost::detail::empty_base<T> >

include/boost/utility/detail/result_of_iterate.hpp

@@ -22,7 +22,7 @@
 # define BOOST_RESULT_OF_ARGS BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)
 #endif
 
-#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x551))
+#if !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x551))
 template<typename F BOOST_PP_ENUM_TRAILING_PARAMS(BOOST_PP_ITERATION(),typename T)>
 struct tr1_result_of<F(BOOST_RESULT_OF_ARGS)>
     : conditional<
@@ -151,7 +151,7 @@ struct cpp0x_result_of_impl<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)),
 
 #else // defined(BOOST_RESULT_OF_USE_DECLTYPE) || defined(BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK)
 
-#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x551))
+#if !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x551))
 template<typename F BOOST_PP_ENUM_TRAILING_PARAMS(BOOST_PP_ITERATION(),typename T)>
 struct result_of<F(BOOST_RESULT_OF_ARGS)>
     : tr1_result_of<F(BOOST_RESULT_OF_ARGS)> { };
@@ -177,7 +177,7 @@ struct tr1_result_of_impl<R (&)(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)), F
   typedef R type;
 };
 
-#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x551))
+#if !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x551))
 template<typename R, typename FArgs BOOST_PP_ENUM_TRAILING_PARAMS(BOOST_PP_ITERATION(),typename T)>
 struct tr1_result_of_impl<R (T0::*)
                      (BOOST_PP_ENUM_SHIFTED_PARAMS(BOOST_PP_ITERATION(),T)),

include/boost/utility/value_init.hpp

@@ -1,4 +1,5 @@
 // (C) Copyright 2002-2008, Fernando Luis Cacciola Carballal.
+// Copyright 2020 Peter Dimov
 //
 // Distributed under the Boost Software License, Version 1.0. (See
 // accompanying file LICENSE_1_0.txt or copy at
@@ -21,15 +22,10 @@
 // issues, by clearing the bytes of T, before constructing the T object it
 // contains. More details on these issues are at libs/utility/value_init.htm
 
-#include <boost/aligned_storage.hpp>
 #include <boost/config.hpp> // For BOOST_NO_COMPLETE_VALUE_INITIALIZATION.
-#include <boost/detail/workaround.hpp>
-#include <boost/static_assert.hpp>
-#include <boost/type_traits/cv_traits.hpp>
-#include <boost/type_traits/alignment_of.hpp>
 #include <boost/swap.hpp>
 #include <cstring>
-#include <new>
+#include <cstddef>
 
 #ifdef BOOST_MSVC
 #pragma warning(push)
@@ -60,92 +56,58 @@
 
 namespace boost {
 
+namespace detail {
+
+  struct zero_init
+  {
+    zero_init()
+    {
+    }
+
+    zero_init( void * p, std::size_t n )
+    {
+      std::memset( p, 0, n );
+    }
+  };
+
+} // namespace detail
+
 template<class T>
 class initialized
+#if BOOST_DETAIL_VALUE_INIT_WORKAROUND
+  : detail::zero_init
+#endif
 {
-  private :
-    struct wrapper
-    {
-#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592))
-      typename
-#endif 
-      remove_const<T>::type data;
+  private:
 
-      BOOST_GPU_ENABLED
-      wrapper()
-      :
-      data()
-      {
-      }
-
-      BOOST_GPU_ENABLED
-      wrapper(T const & arg)
-      :
-      data(arg)
-      {
-      }
-    };
-
-    mutable
-#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592))
-      typename
-#endif 
-      aligned_storage<sizeof(wrapper), alignment_of<wrapper>::value>::type x;
-
-    BOOST_GPU_ENABLED
-    wrapper * wrapper_address() const
-    {
-      return static_cast<wrapper *>( static_cast<void*>(&x));
-    }
+    T data_;
 
   public :
 
     BOOST_GPU_ENABLED
-    initialized()
-    {
+    initialized():
 #if BOOST_DETAIL_VALUE_INIT_WORKAROUND
-      std::memset(&x, 0, sizeof(x));
+      zero_init( &const_cast< char& >( reinterpret_cast<char const volatile&>( data_ ) ), sizeof( data_ ) ),
 #endif
-      new (wrapper_address()) wrapper();
+      data_()
+    {
     }
 
     BOOST_GPU_ENABLED
-    initialized(initialized const & arg)
+    explicit initialized(T const & arg): data_( arg )
     {
-      new (wrapper_address()) wrapper( static_cast<wrapper const &>(*(arg.wrapper_address())));
-    }
-
-    BOOST_GPU_ENABLED
-    explicit initialized(T const & arg)
-    {
-      new (wrapper_address()) wrapper(arg);
-    }
-
-    BOOST_GPU_ENABLED
-    initialized & operator=(initialized const & arg)
-    {
-      // Assignment is only allowed when T is non-const.
-      BOOST_STATIC_ASSERT( ! is_const<T>::value );
-      *wrapper_address() = static_cast<wrapper const &>(*(arg.wrapper_address()));
-      return *this;
-    }
-
-    BOOST_GPU_ENABLED
-    ~initialized()
-    {
-      wrapper_address()->wrapper::~wrapper();
     }
 
     BOOST_GPU_ENABLED
     T const & data() const
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
     BOOST_GPU_ENABLED
     T& data()
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
     BOOST_GPU_ENABLED
@@ -157,13 +119,13 @@ class initialized
     BOOST_GPU_ENABLED
     operator T const &() const
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
     BOOST_GPU_ENABLED
     operator T&()
     {
-      return wrapper_address()->data;
+      return data_;
     }
 
 } ;

operators.htm

@@ -454,7 +454,7 @@ const point<float> pi_over_4_normalized = pi_over_4 / length(pi_over_4);
       </caption>
 
       <tr>
-        <td colspan="3">
+        <td colspan="4">
           <table align="center" border="1">
             <caption>
               <em>Key</em>
@@ -482,6 +482,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <th>Supplied Operations</th>
 
         <th>Requirements</th>
+
+        <th>Propagates <code>constexpr</code>?</th>
       </tr>
 
       <tr>
@@ -496,6 +498,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>t &lt; t1</code>.<br>
          Return convertible to <code>bool</code>. See the <a href=
         "#ordering">Ordering Note</a>.</td>
+
+        <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
 
       <tr>
@@ -513,6 +518,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>t &lt; u</code>. <code>t &gt; u</code>.<br>
          Returns convertible to <code>bool</code>. See the <a href=
         "#ordering">Ordering Note</a>.</td>
+
+        <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
 
       <tr>
@@ -524,6 +532,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
 
         <td><code>t == t1</code>.<br>
          Return convertible to <code>bool</code>.</td>
+
+        <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
 
       <tr>
@@ -537,6 +548,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
 
         <td><code>t == u</code>.<br>
          Return convertible to <code>bool</code>.</td>
+
+         <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
 
       <tr>
@@ -548,6 +562,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp += t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -560,6 +576,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp += u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -572,6 +590,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp -= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -584,6 +604,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp -= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -594,6 +616,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
 
         <td><code>T temp(u); temp -= t</code>.<br>
          Return convertible to <code>T</code>.</td>
+
+         <td>No</td>
       </tr>
 
       <tr>
@@ -606,6 +630,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp *= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -619,6 +645,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp *= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -630,6 +658,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp /= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -641,6 +671,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp /= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -651,6 +683,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
 
         <td><code>T temp(u); temp /= t</code>.<br>
          Return convertible to <code>T</code>.</td>
+
+         <td>No</td>
       </tr>
 
       <tr>
@@ -662,6 +696,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp %= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -673,6 +709,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp %= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -683,6 +721,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
 
         <td><code>T temp(u); temp %= t</code>.<br>
          Return convertible to <code>T</code>.</td>
+
+         <td>No</td>
       </tr>
 
       <tr>
@@ -694,6 +734,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp |= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -706,6 +748,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp |= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -717,6 +761,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp &amp;= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -729,6 +775,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp &amp;= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -740,6 +788,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp ^= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -752,6 +802,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp ^= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -762,6 +814,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
 
         <td><code>T temp(t); ++t</code><br>
          Return convertible to <code>T</code>.</td>
+
+         <td>No</td>
       </tr>
 
       <tr>
@@ -772,6 +826,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
 
         <td><code>T temp(t); --t;</code><br>
          Return convertible to <code>T</code>.</td>
+
+         <td>No</td>
       </tr>
 
       <tr>
@@ -784,6 +840,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp &lt;&lt;= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -796,6 +854,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp &lt;&lt;= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -808,6 +868,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp &gt;&gt;= t1</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -820,6 +882,8 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>T temp(t); temp &gt;&gt;= u</code>.<br>
          Return convertible to <code>T</code>. See the <a href=
         "#symmetry">Symmetry Note</a>.</td>
+
+        <td>No</td>
       </tr>
 
       <tr>
@@ -831,6 +895,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>t &lt; t1</code>.<br>
          Return convertible to <code>bool</code>. See the <a href=
         "#ordering">Ordering Note</a>.</td>
+
+        <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
 
       <tr>
@@ -842,6 +909,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>t &lt; u</code>. <code>t &gt; u</code>.<br>
          Returns convertible to <code>bool</code>. See the <a href=
         "#ordering">Ordering Note</a>.</td>
+
+        <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
 
       <tr>
@@ -856,6 +926,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         <td><code>t &lt; t1</code>. <code>t == t1</code>.<br>
          Returns convertible to <code>bool</code>. See the <a href=
         "#ordering">Ordering Note</a>.</td>
+
+        <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
 
       <tr>
@@ -874,6 +947,9 @@ const point&lt;float&gt; pi_over_4_normalized = pi_over_4 / length(pi_over_4);
         u</code>.<br>
          Returns convertible to <code>bool</code>. See the <a href=
         "#ordering">Ordering Note</a>.</td>
+
+        <td>Since <code>C++11</code><br>
+        <span style="font-size:small;">(except <a href="https://developercommunity.visualstudio.com/content/problem/414193/rejects-valid-constexpr-marked-friend-function-def.html">MSVC &lt; v19.22</a>)</span></td>
       </tr>
     </table>
 

test/Jamfile.v2

@@ -21,6 +21,7 @@ run compressed_pair_final_test.cpp ;
 run iterators_test.cpp ;
 
 run operators_test.cpp ;
+compile operators_constexpr_test.cpp ;
 
 compile result_of_test.cpp ;
 
@@ -35,6 +36,8 @@ run string_view_test2.cpp ;
 run string_view_test_io.cpp ;
 
 run value_init_test.cpp ;
+run value_init_test2.cpp ;
+run value_init_test3.cpp ;
 run value_init_workaround_test.cpp ;
 run initialized_test.cpp ;
 compile-fail value_init_test_fail1.cpp ;

test/call_traits_test.cpp

@@ -376,7 +376,7 @@ void call_traits_test<T, true>::assert_construct(typename boost::call_traits<T>:
    reference r = t;
    const_reference cr = t;
    reference r2 = r;
-   #ifndef __BORLANDC__
+   #ifndef BOOST_BORLANDC
    // C++ Builder buglet:
    const_reference cr2 = r;
    #endif
@@ -393,7 +393,7 @@ void call_traits_test<T, true>::assert_construct(typename boost::call_traits<T>:
    unused_variable(v3);
    unused_variable(v4);
    unused_variable(v5);
-#ifndef __BORLANDC__
+#ifndef BOOST_BORLANDC
    unused_variable(r2);
    unused_variable(cr2);
 #endif

test/operators_constexpr_test.cpp

@@ -0,0 +1,59 @@
+/*
+Copyright 2020 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+
+#include <boost/config.hpp>
+#if !defined(BOOST_NO_CXX11_CONSTEXPR) && \
+    (!defined(BOOST_MSVC) || (BOOST_MSVC >= 1922))
+#include <boost/operators.hpp>
+#include <boost/static_assert.hpp>
+
+namespace {
+
+class Value
+    : boost::operators<Value> {
+public:
+    BOOST_OPERATORS_CONSTEXPR explicit Value(int v)
+        : v_(v) { }
+
+    BOOST_OPERATORS_CONSTEXPR bool
+    operator<(const Value& x) const {
+        return v_ < x.v_;
+    }
+
+    BOOST_OPERATORS_CONSTEXPR bool
+    operator==(const Value& x) const {
+        return v_ == x.v_;
+    }
+
+private:
+    int v_;
+};
+
+} // namespace
+
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(1) == Value(2)));
+BOOST_STATIC_ASSERT(Value(1) != Value(2));
+BOOST_STATIC_ASSERT(Value(1) < Value(2));
+BOOST_STATIC_ASSERT(Value(1) <= Value(2));
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(1) > Value(2)));
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(1) >= Value(2)));
+
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(2) == Value(1)));
+BOOST_STATIC_ASSERT(Value(2) != Value(1));
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(2) < Value(1)));
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(2) <= Value(1)));
+BOOST_STATIC_ASSERT(Value(2) >  Value(1));
+BOOST_STATIC_ASSERT(Value(2) >= Value(1));
+
+BOOST_STATIC_ASSERT(Value(1) == Value(1));
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(1) != Value(1)));
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(1) < Value(1)));
+BOOST_STATIC_ASSERT(Value(1) <= Value(1));
+BOOST_STATIC_ASSERT(!static_cast<bool>(Value(1) > Value(1)));
+BOOST_STATIC_ASSERT(Value(1) >= Value(1));
+#endif

test/operators_test.cpp

@@ -50,9 +50,9 @@ namespace
         void operator!() const;
 
     public:
-        convertible_to_bool( const bool value ) : _value( value ) {}
+         convertible_to_bool( const bool value ) : _value( value ) {}
 
-        operator unspecified_bool_type() const
+         operator unspecified_bool_type() const
           { return _value ? &convertible_to_bool::_value : 0; }
     };
 
@@ -64,12 +64,12 @@ namespace
         , boost::shiftable<Wrapped1<T> >
     {
     public:
-        explicit Wrapped1( T v = T() ) : _value(v) {}
-        T value() const { return _value; }
+         explicit Wrapped1( T v = T() ) : _value(v) {}
+         T value() const { return _value; }
 
-        convertible_to_bool operator<(const Wrapped1& x) const
+         convertible_to_bool operator<(const Wrapped1& x) const
           { return _value < x._value; }
-        convertible_to_bool operator==(const Wrapped1& x) const
+         convertible_to_bool operator==(const Wrapped1& x) const
           { return _value == x._value; }
         
         Wrapped1& operator+=(const Wrapped1& x)
@@ -92,8 +92,8 @@ namespace
           { _value <<= x._value; return *this; }
         Wrapped1& operator>>=(const Wrapped1& x)
           { _value >>= x._value; return *this; }
-        Wrapped1& operator++()               { ++_value; return *this; }
-        Wrapped1& operator--()               { --_value; return *this; }
+        Wrapped1& operator++() { ++_value; return *this; }
+        Wrapped1& operator--() { --_value; return *this; }
         
     private:
         T _value;
@@ -568,6 +568,25 @@ namespace
         int v;
     };
 
+    // Test type designed specifically to test C++20 operator rewriting support
+    struct my_int :
+        public boost::equality_comparable2< my_int, int >
+    {
+        explicit my_int(int n) : m_n(n) {}
+
+        operator int () const
+        {
+            return m_n;
+        }
+
+        bool operator== (my_int that)
+        {
+            return that.m_n == m_n;
+        }
+
+        int m_n;
+    };
+
 } // unnamed namespace
 
 
@@ -932,5 +951,11 @@ main()
 
     cout << "Performed tests on MyLongInt objects.\n";
 
+    my_int my_n = my_int(10);
+
+    // Test if C++20 operator rewriting causes infinite recursion (https://github.com/boostorg/utility/issues/65)
+    BOOST_TEST(my_n == 10);
+    BOOST_TEST(my_n != 20);
+
     return boost::report_errors();
 }

test/value_init_test.cpp

@@ -17,11 +17,12 @@
 
 #include "boost/utility/value_init.hpp"
 
-#ifdef __BORLANDC__
+#ifdef BOOST_BORLANDC
 #pragma hdrstop
 #endif
 
 #include <boost/core/lightweight_test.hpp>
+#include <boost/config/workaround.hpp>
 
 //
 // Sample POD type
@@ -217,8 +218,8 @@ void check_initialized_value ( T const& y )
   BOOST_TEST ( y == initializedValue ) ;
 }
 
-#ifdef  __BORLANDC__
-#if __BORLANDC__ == 0x582
+#ifdef  BOOST_BORLANDC
+#if BOOST_BORLANDC == 0x582
 void check_initialized_value( NonPOD const& )
 {
   // The initialized_value check is skipped for Borland 5.82

test/value_init_test2.cpp

@@ -0,0 +1,169 @@
+// Copyright 2010, Niels Dekker.
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// Test program for the boost::value_initialized<T> workaround.
+//
+// 17 June 2010 (Created) Niels Dekker
+
+#include <boost/utility/value_init.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config/workaround.hpp>
+#include <iostream>
+
+namespace
+{
+  struct empty_struct
+  {
+  };
+
+  // A POD aggregate struct derived from an empty struct.
+  // Similar to struct Foo1 from Microsoft Visual C++ bug report 484295,
+  // "VC++ does not value-initialize members of derived classes without 
+  // user-declared constructor", reported in 2009 by Sylvester Hesp:
+  // https://connect.microsoft.com/VisualStudio/feedback/details/484295
+  struct derived_struct: empty_struct
+  {
+    int data;
+  };
+
+  bool is_value_initialized(const derived_struct& arg)
+  {
+    return arg.data == 0;
+  }
+
+
+  class virtual_destructor_holder
+  {
+  public:
+    int i;
+    virtual ~virtual_destructor_holder()
+    {
+    }
+  };
+
+  bool is_value_initialized(const virtual_destructor_holder& arg)
+  {
+    return arg.i == 0;
+  }
+
+  // Equivalent to the Stats class from GCC Bug 33916,
+  // "Default constructor fails to initialize array members", reported in 2007 by
+  // Michael Elizabeth Chastain: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916
+  // and fixed for GCC 4.2.4.
+  class private_int_array_pair
+  {
+    friend bool is_value_initialized(const private_int_array_pair& arg);
+  private:
+    int first[12];
+    int second[12];
+  };
+
+  bool is_value_initialized(const private_int_array_pair& arg)
+  {
+    for ( unsigned i = 0; i < 12; ++i)
+    {
+      if ( (arg.first[i] != 0) || (arg.second[i] != 0) )
+      {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  struct int_pair_struct
+  {
+    int first;
+    int second;
+  };
+
+  typedef int int_pair_struct::*ptr_to_member_type;
+
+  struct ptr_to_member_struct
+  {
+    ptr_to_member_type data;
+  };
+
+  bool is_value_initialized(const ptr_to_member_struct& arg)
+  {
+    return arg.data == 0;
+  }
+
+  template <typename T>
+  bool is_value_initialized(const T(& arg)[2])
+  {
+    return
+      is_value_initialized(arg[0]) &&
+      is_value_initialized(arg[1]);
+  }
+
+  template <typename T>
+  bool is_value_initialized(const boost::value_initialized<T>& arg)
+  {
+    return is_value_initialized(arg.data());
+  }
+
+  // Returns zero when the specified object is value-initializated, and one otherwise.
+  // Prints a message to standard output if the value-initialization has failed.
+  template <class T>
+  unsigned failed_to_value_initialized(const T& object, const char *const object_name)
+  {
+    if ( is_value_initialized(object) )
+    {
+      return 0u;
+    }
+    else
+    {
+      std::cout << "Note: Failed to value-initialize " << object_name << '.' << std::endl;
+      return 1u;
+    }
+  }
+
+// A macro that passed both the name and the value of the specified object to
+// the function above here.
+#define FAILED_TO_VALUE_INITIALIZE(value) failed_to_value_initialized(value, #value)
+
+  // Equivalent to the dirty_stack() function from GCC Bug 33916,
+  // "Default constructor fails to initialize array members", reported in 2007 by
+  // Michael Elizabeth Chastain: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916
+  void dirty_stack()
+  {
+    unsigned char array_on_stack[4096];
+    for (unsigned i = 0; i < sizeof(array_on_stack); ++i)
+    {
+      array_on_stack[i] = 0x11;
+    }
+  }
+
+}
+
+
+int main()
+{
+#ifdef BOOST_DETAIL_VALUE_INIT_WORKAROUND_SUGGESTED
+
+  std::cout << "BOOST_DETAIL_VALUE_INIT_WORKAROUND_SUGGESTED is defined.\n\n";
+
+#endif
+
+  dirty_stack();
+
+  BOOST_TEST( is_value_initialized( boost::value_initialized<derived_struct>() ) );
+  BOOST_TEST( is_value_initialized( boost::value_initialized<virtual_destructor_holder[2]>() ) );
+  BOOST_TEST( is_value_initialized( boost::value_initialized<private_int_array_pair>() ) );
+
+#if !BOOST_WORKAROUND( BOOST_MSVC, BOOST_TESTED_AT(1925) )
+
+  // Null pointers to data members are represented as -1 in MSVC, but
+  // value initialization sets them to all zero. The workaround employed
+  // by value_initialized<> is to memset the storage to all zero, which
+  // doesn't help.
+
+  BOOST_TEST( is_value_initialized( boost::value_initialized<ptr_to_member_struct>() ) );
+
+#endif
+
+  return boost::report_errors();
+}

test/value_init_test3.cpp

@@ -0,0 +1,40 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/utility/value_init.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if __cplusplus >= 201103L || ( defined(BOOST_MSVC) && BOOST_MSVC >= 1900 )
+
+struct X
+{
+    int a;
+    char b;
+};
+
+struct Y: boost::value_initialized<X>
+{
+    char c = 42;
+};
+
+int main()
+{
+    Y y;
+
+    BOOST_TEST_EQ( y.data().a, 0 );
+    BOOST_TEST_EQ( y.data().b, 0 );
+    BOOST_TEST_EQ( y.c, 42 );
+
+    return boost::report_errors();
+}
+
+#else
+
+BOOST_PRAGMA_MESSAGE( "Skipping test because compiler doesn't support in-class member initializers" )
+
+int main() {}
+
+#endif

test/value_init_test_fail1.cpp

@@ -13,7 +13,7 @@
 
 #include "boost/utility/value_init.hpp"
 
-#ifdef __BORLANDC__
+#ifdef BOOST_BORLANDC
 #pragma hdrstop
 #endif
 

test/value_init_test_fail2.cpp

@@ -13,7 +13,7 @@
 
 #include "boost/utility/value_init.hpp"
 
-#ifdef __BORLANDC__
+#ifdef BOOST_BORLANDC
 #pragma hdrstop
 #endif
 

test/value_init_test_fail3.cpp

@@ -13,7 +13,7 @@
 
 #include "boost/utility/value_init.hpp"
 
-#ifdef __BORLANDC__
+#ifdef BOOST_BORLANDC
 #pragma hdrstop
 #endif