From 204bcce9df03cedcb298aa916d0b3c64bec28b56 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Wed, 6 Mar 2019 00:26:55 +0200
Subject: [PATCH] Make relational operators constexpr; add
 test/variant_eq_ne_cx.cpp

---
 include/boost/variant2/variant.hpp |  8 +--
 test/Jamfile                       |  3 +
 test/variant_eq_ne_cx.cpp          | 98 ++++++++++++++++++++++++++++++
 3 files changed, 105 insertions(+), 4 deletions(-)
 create mode 100644 test/variant_eq_ne_cx.cpp

diff --git a/include/boost/variant2/variant.hpp b/include/boost/variant2/variant.hpp
index 7ecc25f..3cf2dc1 100644
--- a/include/boost/variant2/variant.hpp
+++ b/include/boost/variant2/variant.hpp
@@ -1562,7 +1562,7 @@ template<class... T> struct eq_L
     variant<T...> const & v;
     variant<T...> const & w;
 
-    template<class I> bool operator()( I i ) const
+    template<class I> constexpr bool operator()( I i ) const
     {
         return v._get_impl( i ) == w._get_impl( i );
     }
@@ -1583,7 +1583,7 @@ template<class... T> struct ne_L
     variant<T...> const & v;
     variant<T...> const & w;
 
-    template<class I> bool operator()( I i ) const
+    template<class I> constexpr bool operator()( I i ) const
     {
         return v._get_impl( i ) != w._get_impl( i );
     }
@@ -1604,7 +1604,7 @@ template<class... T> struct lt_L
     variant<T...> const & v;
     variant<T...> const & w;
 
-    template<class I> bool operator()( I i ) const
+    template<class I> constexpr bool operator()( I i ) const
     {
         return v._get_impl( i ) < w._get_impl( i );
     }
@@ -1630,7 +1630,7 @@ template<class... T> struct le_L
     variant<T...> const & v;
     variant<T...> const & w;
 
-    template<class I> bool operator()( I i ) const
+    template<class I> constexpr bool operator()( I i ) const
     {
         return v._get_impl( i ) <= w._get_impl( i );
     }
diff --git a/test/Jamfile b/test/Jamfile
index 714f5e2..89be6a9 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -57,7 +57,10 @@ run variant_emplace_type.cpp ;
 compile variant_emplace_type_cx.cpp : [ requires cxx14_constexpr ] ;
 
 run variant_swap.cpp ;
+
 run variant_eq_ne.cpp ;
+compile variant_eq_ne_cx.cpp : [ requires cxx14_constexpr ] ;
+
 run variant_destroy.cpp ;
 run variant_visit.cpp ;
 run variant_lt_gt.cpp ;
diff --git a/test/variant_eq_ne_cx.cpp b/test/variant_eq_ne_cx.cpp
new file mode 100644
index 0000000..9ebb751
--- /dev/null
+++ b/test/variant_eq_ne_cx.cpp
@@ -0,0 +1,98 @@
+
+// Copyright 2017, 2019 Peter Dimov
+//
+// 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/variant2/variant.hpp>
+using namespace boost::variant2;
+
+#if !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
+#include <boost/config/pragma_message.hpp>
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr op==, op!= test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+
+int main() {}
+
+#else
+
+struct X
+{
+};
+
+inline constexpr bool operator==( X const&, X const& ) { return false; }
+inline constexpr bool operator!=( X const&, X const& ) { return false; }
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    {
+        constexpr variant<int> v1, v2, v3( 1 ), v4( 1 );
+
+        STATIC_ASSERT( v1 == v2 );
+        STATIC_ASSERT( !(v1 != v2) );
+
+        STATIC_ASSERT( v1 != v3 );
+        STATIC_ASSERT( !(v1 == v3) );
+
+        STATIC_ASSERT( v3 == v4 );
+        STATIC_ASSERT( !(v3 != v4) );
+    }
+
+    {
+        constexpr variant<int, float> v1, v2, v3( 1 ), v4( 1 ), v5( 3.14f ), v6( 3.14f );
+
+        STATIC_ASSERT( v1 == v2 );
+        STATIC_ASSERT( !(v1 != v2) );
+
+        STATIC_ASSERT( v1 != v3 );
+        STATIC_ASSERT( !(v1 == v3) );
+
+        STATIC_ASSERT( v3 == v4 );
+        STATIC_ASSERT( !(v3 != v4) );
+
+        STATIC_ASSERT( v1 != v5 );
+        STATIC_ASSERT( !(v1 == v5) );
+
+        STATIC_ASSERT( v3 != v5 );
+        STATIC_ASSERT( !(v3 == v5) );
+
+        STATIC_ASSERT( v5 == v6 );
+        STATIC_ASSERT( !(v5 != v6) );
+    }
+
+    {
+        constexpr variant<int, int, float> v1, v2, v3( in_place_index_t<1>{} ), v4( in_place_index_t<1>{} ), v5( 3.14f ), v6( 3.14f );
+
+        STATIC_ASSERT( v1 == v2 );
+        STATIC_ASSERT( !(v1 != v2) );
+
+        STATIC_ASSERT( v1 != v3 );
+        STATIC_ASSERT( !(v1 == v3) );
+
+        STATIC_ASSERT( v3 == v4 );
+        STATIC_ASSERT( !(v3 != v4) );
+
+        STATIC_ASSERT( v1 != v5 );
+        STATIC_ASSERT( !(v1 == v5) );
+
+        STATIC_ASSERT( v3 != v5 );
+        STATIC_ASSERT( !(v3 == v5) );
+
+        STATIC_ASSERT( v5 == v6 );
+        STATIC_ASSERT( !(v5 != v6) );
+    }
+
+    {
+        constexpr variant<X> v1, v2;
+
+        STATIC_ASSERT( !(v1 == v2) );
+        STATIC_ASSERT( !(v1 != v2) );
+    }
+}
+
+#endif