From c5c49894e6b870c7403bf95041fcd5218a6f1b3a Mon Sep 17 00:00:00 2001
From: Klemens <klemens.d.morgenstern@gmail.com>
Date: Wed, 8 Mar 2023 08:07:38 +0800
Subject: [PATCH] Made result::error movable.

Closes #108.
---
 doc/system/reference.adoc       |   3 +-
 include/boost/system/result.hpp |  16 ++++-
 test/CMakeLists.txt             |   1 +
 test/Jamfile.v2                 |   1 +
 test/result_error_move.cpp      | 108 ++++++++++++++++++++++++++++++++
 5 files changed, 126 insertions(+), 3 deletions(-)
 create mode 100644 test/result_error_move.cpp

diff --git a/doc/system/reference.adoc b/doc/system/reference.adoc
index d5ab46f..798cc75 100644
--- a/doc/system/reference.adoc
+++ b/doc/system/reference.adoc
@@ -1657,7 +1657,8 @@ public:
 
     // error access
 
-    constexpr E error() const;
+    constexpr E error() const &;
+    constexpr E error() &&;
 
     // emplace
 
diff --git a/include/boost/system/result.hpp b/include/boost/system/result.hpp
index 4084ca8..08eb899 100644
--- a/include/boost/system/result.hpp
+++ b/include/boost/system/result.hpp
@@ -401,12 +401,18 @@ public:
 
     // error access
 
-    constexpr E error() const
+    constexpr E error() const &
         noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_copy_constructible<E>::value )
     {
         return has_error()? variant2::unsafe_get<1>( v_ ): E();
     }
 
+    BOOST_CXX14_CONSTEXPR E error() &&
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_move_constructible<E>::value )
+    {
+        return has_error()? std::move( variant2::unsafe_get<1>( v_ ) ): E();
+    }
+
     // emplace
 
     template<class... A>
@@ -581,12 +587,18 @@ public:
 
     // error access
 
-    constexpr E error() const
+    constexpr E error() const &
         noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_copy_constructible<E>::value )
     {
         return has_error()? variant2::unsafe_get<1>( v_ ): E();
     }
 
+    BOOST_CXX14_CONSTEXPR E error() &&
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_move_constructible<E>::value )
+    {
+        return has_error()? std::move( variant2::unsafe_get<1>( v_ ) ): E();
+    }
+
     // emplace
 
     BOOST_CXX14_CONSTEXPR void emplace()
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index ff166a6..7bc6d67 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -163,3 +163,4 @@ boost_test(TYPE run SOURCES result_emplace.cpp)
 boost_test(TYPE run SOURCES result_error_construct4.cpp)
 boost_test(TYPE run SOURCES result_value_construct4.cpp)
 boost_test(TYPE run SOURCES result_value_construct5.cpp)
+boost_test(TYPE run SOURCES result_error_move.cpp)
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index df74b5e..139bb23 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -193,3 +193,4 @@ run result_emplace.cpp : : : $(CPP11) ;
 run result_error_construct4.cpp : : : $(CPP11) ;
 run result_value_construct4.cpp : : : $(CPP11) ;
 run result_value_construct5.cpp : : : $(CPP11) ;
+run result_error_move.cpp : : : $(CPP11) ;
diff --git a/test/result_error_move.cpp b/test/result_error_move.cpp
new file mode 100644
index 0000000..771ca75
--- /dev/null
+++ b/test/result_error_move.cpp
@@ -0,0 +1,108 @@
+// Copyright 2023 Klemens Morgenstern
+// 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>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <string>
+
+using namespace boost::system;
+
+struct XM
+{
+    int v_;
+
+    explicit XM( int v = 0 ): v_( v ) {}
+
+    XM( XM const& ) = delete;
+    XM& operator=( XM const& ) = delete;
+    XM( XM && ) = default;
+    XM& operator=( XM && ) = default;
+};
+
+int main()
+{
+    {
+        result<std::string, XM> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<std::string, XM>( 1 ).has_value() ));
+        BOOST_TEST(( result<std::string, XM>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, XM>( 1 ).error().v_), 1 );
+    }
+
+    {
+        result<std::string, XM> r( "s" );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        result<std::string, XM> r( "s" );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        BOOST_TEST(( result<std::string, XM>( "s" ).has_value() ));
+        BOOST_TEST(( !result<std::string, XM>( "s" ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, XM>( "s" ).error().v_), 0 );
+    }
+
+      {
+        result<void, XM> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<void, XM>( 1 ).has_value() ));
+        BOOST_TEST(( result<void, XM>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<void, XM>( 1 ).error().v_), 1 );
+    }
+
+    {
+        result<void, XM> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        result<void, XM> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        BOOST_TEST(( result<void, XM>( ).has_value() ));
+        BOOST_TEST(( !result<void, XM>( ).has_error() ));
+
+        BOOST_TEST_EQ( (result<void, XM>( ).error().v_), 0 );
+    }
+    return boost::report_errors();
+}