Add definitions of ::in_place_* for result specializations. Fixes #115.

.github/workflows/ci.yml

@@ -131,9 +131,15 @@ jobs:
           - toolset: clang
             compiler: clang++-16
             cxxstd: "03,11,14,17,20,2b"
-            os: ubuntu-latest
             container: ubuntu:23.04
+            os: ubuntu-latest
             install: clang-16
+          - toolset: clang
+            compiler: clang++-17
+            cxxstd: "03,11,14,17,20,2b"
+            container: ubuntu:23.10
+            os: ubuntu-latest
+            install: clang-17
           - toolset: clang
             cxxstd: "03,11,14,17,2a"
             os: macos-11

include/boost/system/result.hpp

@@ -450,6 +450,13 @@ public:
     }
 };
 
+#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
+
+template<class T, class E> constexpr in_place_value_t result<T, E>::in_place_value;
+template<class T, class E> constexpr in_place_error_t result<T, E>::in_place_error;
+
+#endif
+
 template<class Ch, class Tr, class T, class E> std::basic_ostream<Ch, Tr>& operator<<( std::basic_ostream<Ch, Tr>& os, result<T, E> const & r )
 {
     if( r.has_value() )
@@ -652,6 +659,13 @@ public:
     }
 };
 
+#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
+
+template<class E> constexpr in_place_value_t result<void, E>::in_place_value;
+template<class E> constexpr in_place_error_t result<void, E>::in_place_error;
+
+#endif
+
 template<class Ch, class Tr, class E> std::basic_ostream<Ch, Tr>& operator<<( std::basic_ostream<Ch, Tr>& os, result<void, E> const & r )
 {
     if( r.has_value() )
@@ -885,6 +899,13 @@ public:
     }
 };
 
+#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
+
+template<class U, class E> constexpr in_place_value_t result<U&, E>::in_place_value;
+template<class U, class E> constexpr in_place_error_t result<U&, E>::in_place_error;
+
+#endif
+
 // operator|
 
 namespace detail

test/CMakeLists.txt

@@ -176,3 +176,4 @@ boost_test(TYPE run SOURCES result_and_fn1v.cpp)
 boost_test(TYPE run SOURCES result_and_fn1r.cpp)
 boost_test(TYPE run SOURCES result_and_eq_fn1v.cpp)
 boost_test(TYPE run SOURCES result_and_eq_fn1r.cpp)
+boost_test(TYPE run SOURCES result_in_place_use.cpp)

test/Jamfile.v2

@@ -206,3 +206,4 @@ run result_and_fn1v.cpp : : : $(CPP11) ;
 run result_and_fn1r.cpp : : : $(CPP11) ;
 run result_and_eq_fn1v.cpp : : : $(CPP11) ;
 run result_and_eq_fn1r.cpp : : : $(CPP11) ;
+run result_in_place_use.cpp : : : $(CPP11) ;

test/result_in_place_use.cpp

@@ -0,0 +1,22 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+template<class T, class U> void test( T const& t, U const& u )
+{
+    BOOST_TEST_NE( static_cast<void const*>( &t ), static_cast<void const*>( &u ) );
+}
+
+int main()
+{
+    using namespace boost::system;
+
+    test( result<int>::in_place_value, result<int>::in_place_error );
+    test( result<void>::in_place_value, result<void>::in_place_error );
+    test( result<int&>::in_place_value, result<int&>::in_place_error );
+
+    return boost::report_errors();
+}