From 54d3b253b13ee1a5c4dcf5c08765215d8d96e695 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 29 Oct 2023 20:57:29 +0200
Subject: [PATCH] Add operator&( result, unary-returning-result )

---
 include/boost/system/result.hpp |  58 +++++-
 test/CMakeLists.txt             |   1 +
 test/Jamfile.v2                 |   1 +
 test/result_and_fn0r.cpp        | 347 ++++++++++++++++++++++++++++++++
 4 files changed, 397 insertions(+), 10 deletions(-)
 create mode 100644 test/result_and_fn0r.cpp

diff --git a/include/boost/system/result.hpp b/include/boost/system/result.hpp
index 4490cb6..82dbe2a 100644
--- a/include/boost/system/result.hpp
+++ b/include/boost/system/result.hpp
@@ -915,7 +915,7 @@ template<class T, class E> struct is_result< result<T, E> >: std::true_type {};
 template<class T, class E, class U,
     class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
 >
-    T operator|( result<T, E> const& r, U&& u )
+T operator|( result<T, E> const& r, U&& u )
 {
     if( r )
     {
@@ -930,7 +930,7 @@ template<class T, class E, class U,
 template<class T, class E, class U,
     class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
 >
-    T operator|( result<T, E>&& r, U&& u )
+T operator|( result<T, E>&& r, U&& u )
 {
     if( r )
     {
@@ -948,7 +948,7 @@ template<class T, class E, class F,
     class U = decltype( std::declval<F>()() ),
     class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
 >
-    T operator|( result<T, E> const& r, F&& f )
+T operator|( result<T, E> const& r, F&& f )
 {
     if( r )
     {
@@ -964,7 +964,7 @@ template<class T, class E, class F,
     class U = decltype( std::declval<F>()() ),
     class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
 >
-    T operator|( result<T, E>&& r, F&& f )
+T operator|( result<T, E>&& r, F&& f )
 {
     if( r )
     {
@@ -983,7 +983,7 @@ template<class T, class E, class F,
     class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
     class En2 = typename std::enable_if<detail::is_value_convertible_to<T, typename U::value_type>::value>::type
 >
-    U operator|( result<T, E> const& r, F&& f )
+U operator|( result<T, E> const& r, F&& f )
 {
     if( r )
     {
@@ -1000,7 +1000,7 @@ template<class T, class E, class F,
     class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
     class En2 = typename std::enable_if<detail::is_value_convertible_to<T, typename U::value_type>::value>::type
 >
-    U operator|( result<T, E>&& r, F&& f )
+U operator|( result<T, E>&& r, F&& f )
 {
     if( r )
     {
@@ -1017,7 +1017,7 @@ template<class E, class F,
     class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
     class En2 = typename std::enable_if<std::is_void<typename U::value_type>::value>::type
 >
-    U operator|( result<void, E> const& r, F&& f )
+U operator|( result<void, E> const& r, F&& f )
 {
     if( r )
     {
@@ -1034,7 +1034,7 @@ template<class E, class F,
     class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
     class En2 = typename std::enable_if<std::is_void<typename U::value_type>::value>::type
 >
-    U operator|( result<void, E>&& r, F&& f )
+U operator|( result<void, E>&& r, F&& f )
 {
     if( r )
     {
@@ -1046,13 +1046,15 @@ template<class E, class F,
     }
 }
 
+// operator&
+
 // result & unary-returning-value
 
 template<class T, class E, class F,
     class U = decltype( std::declval<F>()( std::declval<T const&>() ) ),
     class En = typename std::enable_if<!detail::is_result<U>::value>::type
 >
-    result<U, E> operator&( result<T, E> const& r, F&& f )
+result<U, E> operator&( result<T, E> const& r, F&& f )
 {
     if( r )
     {
@@ -1068,7 +1070,43 @@ template<class T, class E, class F,
     class U = decltype( std::declval<F>()( std::declval<T>() ) ),
     class En = typename std::enable_if<!detail::is_result<U>::value>::type
 >
-    result<U, E> operator&( result<T, E>&& r, F&& f )
+result<U, E> operator&( result<T, E>&& r, F&& f )
+{
+    if( r )
+    {
+        return std::forward<F>( f )( *std::move( r ) );
+    }
+    else
+    {
+        return r.error();
+    }
+}
+
+// result & unary-returning-result
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T const&>() ) ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_convertible<E, typename U::error_type>::value>::type
+>
+U operator&( result<T, E> const& r, F&& f )
+{
+    if( r )
+    {
+        return std::forward<F>( f )( *r );
+    }
+    else
+    {
+        return r.error();
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T>() ) ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_convertible<E, typename U::error_type>::value>::type
+>
+U operator&( result<T, E>&& r, F&& f )
 {
     if( r )
     {
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 6d4e2b3..12d3064 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -173,3 +173,4 @@ boost_test(TYPE compile-fail SOURCES result_or_value_fail2.cpp)
 boost_test(TYPE run SOURCES result_or_fn0v.cpp)
 boost_test(TYPE run SOURCES result_or_fn0r.cpp)
 boost_test(TYPE run SOURCES result_and_fn0v.cpp)
+boost_test(TYPE run SOURCES result_and_fn0r.cpp)
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 1864c07..d594d7d 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -203,3 +203,4 @@ compile-fail result_or_value_fail2.cpp : $(CPP11) ;
 run result_or_fn0v.cpp : : : $(CPP11) ;
 run result_or_fn0r.cpp : : : $(CPP11) ;
 run result_and_fn0v.cpp : : : $(CPP11) ;
+run result_and_fn0r.cpp : : : $(CPP11) ;
diff --git a/test/result_and_fn0r.cpp b/test/result_and_fn0r.cpp
new file mode 100644
index 0000000..249779a
--- /dev/null
+++ b/test/result_and_fn0r.cpp
@@ -0,0 +1,347 @@
+// Copyright 2017, 2021, 2022 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>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+result<int, E2> fi( int x )
+{
+    return 2 * x + 1;
+}
+
+result<int, E2> fi2( int )
+{
+    return E2();
+}
+
+result<void, E2> fi3( int )
+{
+    return {};
+}
+
+result<X, E2> fy( Y y )
+{
+    return X{ 2 * y.v_ + 1 };
+}
+
+result<X, E2> fy2( Y )
+{
+    return E2();
+}
+
+result<void, E2> fy3( Y )
+{
+    return {};
+}
+
+result<int, E2> fri( int& x )
+{
+    return x * 2 + 1;
+}
+
+result<int&, E2> fri2( int& )
+{
+    return E2();
+}
+
+result<void, E2> fri3( int& )
+{
+    return {};
+}
+
+int main()
+{
+    {
+        result<int, E> r( 1 );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        result<int, E> const r( 1 );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( 1 ) & fi;
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( 1 ) & fi2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int, E>( 1 ) & fi3;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( in_place_error ) & fi;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( in_place_error ) & fi2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int, E>( in_place_error ) & fi3;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2->v_, 3 );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy3;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_error ) & fy;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_error ) & fy2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<Y, E>( in_place_error ) & fy3;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E> r( x1 );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E> const r( x1 );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        int x1 = 1;
+
+        result<int, E2> r2 = result<int&, E>( x1 ) & fri;
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&, E2> r2 = result<int&, E>( x1 ) & fri2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<void, E2> r2 = result<int&, E>( x1 ) & fri3;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int&, E>( in_place_error ) & fri;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E2> r2 = result<int&, E>( in_place_error ) & fri2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int&, E>( in_place_error ) & fri3;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    return boost::report_errors();
+}