Enable pointers to members in r & f, where f returns result<>

include/boost/system/result.hpp

@@ -1269,7 +1269,24 @@ result<U, E> operator&( result<void, E> const& r, F&& f )
 // result & unary-returning-result
 
 template<class T, class E, class F,
-    class U = decltype( std::declval<F>()( std::declval<T const&>() ) ),
+    class U = typename std::decay< detail::invoke_result_t<F, T&> >::type,
+    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.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return detail::invoke( std::forward<F>( f ), *r );
+    }
+}
+
+template<class T, class E, class F,
+    class U = typename std::decay< detail::invoke_result_t<F, T const&> >::type,
     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
 >
@@ -1281,12 +1298,12 @@ U operator&( result<T, E> const& r, F&& f )
     }
     else
     {
-        return std::forward<F>( f )( *r );
+        return detail::invoke( std::forward<F>( f ), *r );
     }
 }
 
 template<class T, class E, class F,
-    class U = decltype( std::declval<F>()( std::declval<T>() ) ),
+    class U = typename std::decay< detail::invoke_result_t<F, T> >::type,
     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
 >
@@ -1298,7 +1315,7 @@ U operator&( result<T, E>&& r, F&& f )
     }
     else
     {
-        return std::forward<F>( f )( *std::move( r ) );
+        return detail::invoke( std::forward<F>( f ), *std::move( r ) );
     }
 }
 

test/CMakeLists.txt

@@ -177,3 +177,4 @@ boost_test(TYPE run SOURCES result_or_eq_fn0v.cpp)
 boost_test(TYPE run SOURCES result_or_eq_fn0r.cpp)
 
 boost_test(TYPE run SOURCES result_and_mfn1v.cpp)
+boost_test(TYPE run SOURCES result_and_mfn1r.cpp)

test/Jamfile.v2

@@ -210,3 +210,4 @@ run result_or_eq_fn0v.cpp ;
 run result_or_eq_fn0r.cpp ;
 
 run result_and_mfn1v.cpp ;
+run result_and_mfn1r.cpp ;

test/result_and_mfn1r.cpp

@@ -0,0 +1,230 @@
+// 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 E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+struct X
+{
+    int v_ = 0;
+    mutable int g_called_ = 0;
+
+    X( int v ): v_( v ) {}
+
+    result<int, E2> f() const { return v_; }
+    result<int, E2> f2() const { return E2(); }
+
+    result<int&, E2> g() { return v_; }
+    result<int const&, E2> g2() const { return v_; }
+
+    result<void, E2> h() const { return {}; }
+    result<void, E2> h2() const { return E2(); }
+};
+
+int main()
+{
+    {
+        result<X, E> r( 1 );
+
+        {
+            result<int, E2> r2 = r & &X::f;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 1 );
+        }
+
+        {
+            result<int, E2> r2 = r & &X::f2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & &X::g;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &r->v_ );
+        }
+
+        {
+            result<int const&, E2> r2 = r & &X::g2;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &r->v_ );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h;
+            BOOST_TEST( r2.has_value() );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h2;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<X, E> const r( 1 );
+
+        {
+            result<int, E2> r2 = r & &X::f;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 1 );
+        }
+
+        {
+            result<int, E2> r2 = r & &X::f2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int const&, E2> r2 = r & &X::g2;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &r->v_ );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h;
+            BOOST_TEST( r2.has_value() );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h2;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        {
+            result<int, E2> r2 = result<X, E>( 1 ) & &X::f;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 1 );
+        }
+
+        {
+            result<int, E2> r2 = result<X, E>( 1 ) & &X::f2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = result<X, E>( 1 ) & &X::g;
+            BOOST_TEST( r2.has_value() );
+        }
+
+        {
+            result<int const&, E2> r2 = result<X, E>( 1 ) & &X::g2;
+            BOOST_TEST( r2.has_value() );
+        }
+
+        {
+            result<void, E2> r2 = result<X, E>( 1 ) & &X::h;
+            BOOST_TEST( r2.has_value() );
+        }
+
+        {
+            result<void, E2> r2 = result<X, E>( 1 ) & &X::h2;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<X, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & &X::f;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & &X::f2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & &X::g;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int const&, E2> r2 = r & &X::g2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h2;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<X, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & &X::f;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & &X::f2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int const&, E2> r2 = r & &X::g2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & &X::h2;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        {
+            result<int, E2> r2 = result<X, E>( in_place_error ) & &X::f;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = result<X, E>( in_place_error ) & &X::f2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = result<X, E>( in_place_error ) & &X::g;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int const&, E2> r2 = result<X, E>( in_place_error ) & &X::g2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = result<X, E>( in_place_error ) & &X::h;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = result<X, E>( in_place_error ) & &X::h2;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    return boost::report_errors();
+}