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

.drone.jsonnet

@@ -226,6 +226,20 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "g++-12-multilib",
     ),
 
+    linux_pipeline(
+        "Linux 23.04 GCC 13 32",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '32' },
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 GCC 13 64",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '64' },
+        "g++-13-multilib",
+    ),
+
     linux_pipeline(
         "Linux 16.04 Clang 3.5",
         "cppalliance/droneubuntu1604:1",
@@ -283,6 +297,13 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         ["deb http://apt.llvm.org/jammy/ llvm-toolchain-jammy-15 main"],
     ),
 
+    linux_pipeline(
+        "Linux 23.04 Clang 16",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-16', CXXSTD: '11,14,17,20,2b' },
+        "clang-16",
+    ),
+
     macos_pipeline(
         "MacOS 10.15 Xcode 12.2 UBSAN",
         { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,1z' } + ubsan,
@@ -293,6 +314,18 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,1z' } + asan,
     ),
 
+    macos_pipeline(
+        "MacOS 12.4 Xcode 13.4.1 UBSAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
+    ),
+
+    macos_pipeline(
+        "MacOS 12.4 Xcode 13.4.1 ASAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,17,20,2b' } + asan,
+        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
+    ),
+
     windows_pipeline(
         "Windows VS2015 msvc-14.0",
         "cppalliance/dronevs2015",

.drone/drone.sh

@@ -5,6 +5,7 @@
 # https://www.boost.org/LICENSE_1_0.txt
 
 set -ex
+export PATH=~/.local/bin:/usr/local/bin:$PATH
 
 DRONE_BUILD_DIR=$(pwd)
 

.github/workflows/ci.yml

@@ -113,24 +113,33 @@ jobs:
           - toolset: clang
             compiler: clang++-13
             cxxstd: "03,11,14,17,20,2b"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: clang-13
           - toolset: clang
             compiler: clang++-14
             cxxstd: "03,11,14,17,20,2b"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: clang-14
           - toolset: clang
             compiler: clang++-15
             cxxstd: "03,11,14,17,20,2b"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: clang-15
           - 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
@@ -213,7 +222,7 @@ jobs:
             addrmd: 32,64
             os: windows-2022
           - toolset: clang-win
-            cxxstd: "14,17,latest"
+            cxxstd: "14,17,20,latest"
             addrmd: 32,64
             os: windows-2022
           - toolset: gcc

doc/system/changes.adoc

@@ -8,6 +8,13 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix:
 
+## Changes in Boost 1.84
+
+* Added support for `result<U&, E>`.
+* Added `operator|` for `result`.
+* Added `operator&` for `result`.
+* Added `operator&=` for `result`.
+
 ## Changes in Boost 1.81
 
 * The macro `BOOST_SYSTEM_DISABLE_THREADS` can now be defined to disable

doc/system/reference.adoc

@@ -1517,6 +1517,38 @@ constexpr in_place_error_t in_place_error{};
 
 template<class T, class E = error_code> class result;
 template<class E> class result<void, E>;
+template<class U, class E> class result<U&, E>;
+
+// operator|
+
+template<class T, class E, class U> T operator|( result<T, E> const& r, U&& u );
+template<class T, class E, class U> T operator|( result<T, E>&& r, U&& u );
+
+template<class T, class E, class F> T operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F> T operator|( result<T, E>&& r, F&& f );
+
+template<class T, class E, class F, class R = ...> R operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator|( result<T, E>&& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E> const& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E>&& r, F&& f );
+
+// operator&
+
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E>&& r, F&& f );
+
+template<class T, class E, class F, class R = ...> R operator&( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator&( result<T, E>&& r, F&& f );
+
+// operator&=
+
+template<class T, class E, class F, class U = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
+
+template<class T, class E, class F, class R = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
 
 } // namespace system
 } // namespace boost
@@ -1713,7 +1745,7 @@ Effects: ::
     ensures that `*this` holds the error `E( std::forward<A>(a)... )`.
   - Otherwise, this constructor does not participate in overload resolution.
 Remarks: ::
-  This constructor is only enabled when `sizeof...(T) > 0`.
+  This constructor is only enabled when `sizeof...(A) > 0`.
 
 ```
 template<class... A>
@@ -1747,7 +1779,7 @@ template<class T2, class E2>
 * {blank}
 +
 Ensures: ::
-  If `r2.has_value()` is `true`, `*this` holds the value `T( *r2 )`, otherwise `*this` holds the value `E( r2.error() )`.
+  If `r2.has_value()` is `true`, `*this` holds the value `T( *r2 )`, otherwise `*this` holds the error `E( r2.error() )`.
 Remarks: ::
   This constructor is only enabled when `std::is_convertible<T2, T>::value && std::is_convertible<E2, E>::value` is `true`.
 
@@ -1759,7 +1791,7 @@ template<class T2, class E2>
 * {blank}
 +
 Ensures: ::
-  If `r2.has_value()` is `true`, `*this` holds the value `T( std::move( *r2 ) )`, otherwise `*this` holds the value `E( r2.error() )`.
+  If `r2.has_value()` is `true`, `*this` holds the value `T( std::move( *r2 ) )`, otherwise `*this` holds the error `E( r2.error() )`.
 Remarks: ::
   This constructor is only enabled when `std::is_convertible<T2, T>::value && std::is_convertible<E2, E>::value` is `true`.
 
@@ -1961,6 +1993,9 @@ public:
     template<class... A>
       constexpr result( in_place_error_t, A&&... a );
 
+    template<class E2>
+      constexpr result( result<void, E2> const& r2 );
+
     // queries
 
     constexpr bool has_value() const noexcept;
@@ -2032,7 +2067,7 @@ Effects: ::
     ensures that `*this` holds the error `E( std::forward<A>(a)... )`.
   - Otherwise, this constructor does not participate in overload resolution.
 Remarks: ::
-  This constructor is only enabled when `sizeof...(T) > 0`.
+  This constructor is only enabled when `sizeof...(A) > 0`.
 
 ```
 template<class... A>
@@ -2056,6 +2091,18 @@ Ensures: ::
 Remarks: ::
   This constructor is only enabled when `std::is_constructible<E, A...>::value` is `true`.
 
+```
+template<class E2>
+  constexpr result( result<void, E2> const& r2 );
+```
+[none]
+* {blank}
++
+Ensures: ::
+  If `r2.has_value()` is `true`, `*this` holds an unspecified value, otherwise `*this` holds the error `E( r2.error() )`.
+Remarks: ::
+  This constructor is only enabled when `std::is_convertible<E2, E>::value` is `true`.
+
 #### Queries
 
 ```
@@ -2201,6 +2248,533 @@ Effects: ::
 Returns: ::
   `os`.
 
+### result<U&, E>
+
+```
+namespace boost {
+namespace system {
+
+template<class U, class E> class result<U&, E>
+{
+public:
+
+    using value_type = U&;
+    using error_type = E;
+
+    static constexpr in_place_value_t in_place_value{};
+    static constexpr in_place_error_t in_place_error{};
+
+    // constructors
+
+    template<class A>
+      constexpr result( A&& a ) noexcept;
+
+    template<class... A>
+      constexpr result( A&&... a );
+
+    template<class A>
+      constexpr result( in_place_value_t, A&& a ) noexcept;
+
+    template<class... A>
+      constexpr result( in_place_error_t, A&&... a );
+
+    template<class U2, class E2>
+      constexpr result( result<U2&, E2> const& r2 );
+
+    // queries
+
+    constexpr bool has_value() const noexcept;
+    constexpr bool has_error() const noexcept;
+    constexpr explicit operator bool() const noexcept;
+
+    // checked value access
+
+    constexpr U& value( boost::source_location const & loc =
+      BOOST_CURRENT_LOCATION ) const;
+
+    // unchecked value access
+
+    constexpr U* operator->() const noexcept;
+    constexpr U& operator*() const noexcept;
+
+    // error access
+
+    constexpr E error() const &;
+    constexpr E error() &&;
+
+    // emplace
+
+    template<class A>
+      constexpr U& emplace( A&& a ) noexcept;
+
+    // swap
+
+    constexpr void swap( result& r );
+    friend constexpr void swap( result & r1, result & r2 );
+
+    // equality
+
+    friend constexpr bool operator==( result const & r1, result const & r2 );
+    friend constexpr bool operator!=( result const & r1, result const & r2 );
+};
+
+} // namespace system
+} // namespace boost
+```
+
+#### Constructors
+
+```
+template<class A>
+  constexpr result( A&& a ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the reference `static_cast<U&>( std::forward<A>(a) )`.
+Remarks: ::
+  This constructor is only enabled when `A` is `B&` and `std::is_convertible<B*, U*>::value` is `true`.
+
+```
+template<class... A>
+  constexpr result( A&&... a );
+```
+[none]
+* {blank}
++
+Effects: ::
+  - If `std::is_constructible<E, A...>::value && !std::is_constructible<U&, A...>::value`,
+    ensures that `*this` holds the error `E( std::forward<A>(a)... )`.
+  - Otherwise, this constructor does not participate in overload resolution.
+Remarks: ::
+  This constructor is only enabled when `sizeof...(A) > 0`.
+
+```
+template<class A>
+  constexpr result( in_place_value_t, A&& a ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the reference `static_cast<U&>( std::forward<A>(a) )`.
+Remarks: ::
+  This constructor is only enabled when `A` is `B&` and `std::is_convertible<B*, U*>::value` is `true`.
+
+```
+template<class... A>
+  constexpr result( in_place_error_t, A&&... a );
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the error `E( std::forward<A>(a)... )`.
+Remarks: ::
+  This constructor is only enabled when `std::is_constructible<E, A...>::value` is `true`.
+
+```
+template<class U2, class E2>
+  constexpr result( result<U2&, E2> const& r2 );
+```
+[none]
+* {blank}
++
+Ensures: ::
+  If `r2.has_value()` is `true`, `*this` holds the reference `static_cast<U&>( *r2 )`, otherwise `*this` holds the error `E( r2.error() )`.
+Remarks: ::
+  This constructor is only enabled when `std::is_convertible<U2*, U*>::value && std::is_convertible<E2, E>::value` is `true`.
+
+#### Queries
+
+```
+constexpr bool has_value() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  `true` when `*this` holds a value, `false` otherwise.
+
+```
+constexpr bool has_error() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  `!has_value()`.
+
+```
+constexpr explicit operator bool() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  `has_value()`.
+
+#### Checked Value Access
+
+```
+constexpr U& value(
+  boost::source_location const & loc = BOOST_CURRENT_LOCATION ) const;
+```
+[none]
+* {blank}
++
+Effects: ::
+  If `*this` holds a reference, returns it. Otherwise,
+  calls `throw_exception_from_error`, passing it a reference to
+  the held error, and `loc`.
+
+#### Unchecked Value Access
+
+```
+constexpr U* operator->() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  If `*this` holds a reference, a pointer to its referent. Otherwise, `nullptr`.
+
+```
+constexpr U& operator*() const noexcept;
+```
+[none]
+* {blank}
++
+Requires: :: `*this` holds a reference.
+Returns: ::
+  `*operator\->()`.
+
+#### Error Access
+
+```
+constexpr E error() const &;
+constexpr E error() &&;
+```
+[none]
+* {blank}
++
+Effects: ::
+  If `*this` holds an error, returns it. Otherwise, returns `E()`.
+
+#### emplace
+
+```
+template<class A>
+  constexpr U& emplace( A&& a ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the reference `static_cast<U&>( std::forward<A>(a)... )`.
+Returns: ::
+  The contained reference.
+Remarks: ::
+  This function is only enabled when `A` is `B&` and `std::is_convertible<B*, U*>::value` is `true`.
+
+#### swap
+
+```
+constexpr void swap( result& r );
+```
+[none]
+* {blank}
++
+Effects: ::
+  Exchanges the contents of `*this` and `r`.
+
+```
+friend constexpr void swap( result & r1, result & r2 );
+```
+[none]
+* {blank}
++
+Effects: ::
+  Exchanges the contents of `r1` and `r2`.
+
+#### Equality
+
+```
+friend constexpr bool operator==( result const & r1, result const & r2 );
+```
+[none]
+* {blank}
++
+Effects: ::
+  - If `r1` holds a reference `t1` and `r2` holds a reference `t2`, returns `t1 == t2`.
+  - If `r1` holds an error `e1` and `r2` holds an error `e2`, returns `e1 == e2`.
+  - Otherwise, returns `false`.
+
+```
+friend constexpr bool operator!=( result const & r1, result const & r2 );
+```
+[none]
+* {blank}
++
+Returns: ::
+  `!( r1 == r2 )`.
+
+### Chaining
+
+#### operator|
+
+```
+template<class T, class E, class U> T operator|( result<T, E> const& r, U&& u );
+template<class T, class E, class U> T operator|( result<T, E>&& r, U&& u );
+```
+[none]
+* {blank}
++
+Returns the value in `r`, or if `r` contains an error, a default value `u`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `*r`.
+  - Otherwise, returns `u`.
+Remarks: ::
+  Only enabled when `U` is convertible to `T`.
+Example: ::
++
+```
+result<int> get_server_port(); // can fail
+
+int get_port()
+{
+    return get_server_port() | 443;
+}
+```
+
+```
+template<class T, class E, class F> T operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F> T operator|( result<T, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the value in `r`, or if `r` contains an error, a default value obtained
+by invoking the function `f`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `*r`.
+  - Otherwise, returns `f()`.
+Remarks: ::
+  Only enabled when `f()` is convertible to `T`.
+Example: ::
++
+```
+result<int> get_server_port(); // can fail
+int get_default_port();
+
+int get_port()
+{
+    return get_server_port() | get_default_port;
+}
+```
++
+Note that the right hand side is `get_default_port` and not `get_default_port()`.
+This is important; spelled this way, the function `get_default_port` is called
+only when `get_server_port_impl()` fails. If it were
++
+```
+    return get_server_port() | get_default_port();
+```
++
+the function would have been called unconditionally.
++
+Another, equivalent, way is to use a lambda
++
+```
+    return get_server_port() | []{ return get_default_port(); };
+```
++
+which isn't necessary here, but would be needed for more complex expressions.
+
+```
+template<class T, class E, class F, class R = ...> R operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator|( result<T, E>&& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E> const& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the value in `r`, or if `r` contains an error, another `result` obtained
+by invoking the function `f`.
++
+Let `R` be the type of `f()`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `*r`.
+  - Otherwise, returns `f()`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result` and `T` is convertible to `R::value_type`.
+Example: ::
++
+```
+result<int> get_server_port(); // can fail
+result<int> get_default_port(); // can fail
+
+int get_port()
+{
+    return get_server_port() | get_default_port | 443;
+}
+```
+
+#### operator&
+
+```
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E> const& r, F&& f );
+
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the error in `r`, or if `r` contains a value, transforms the value by calling `f` on it.
++
+Let `U` be the type of `f(*r)`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `f(*r)`.
+  - Otherwise, returns `r.error()`.
+Remarks: ::
+  Only enabled when `U` is not an instance of `result`.
+Example: ::
++
+```
+struct currency_type
+{
+    char code_[ 4 ] = {};
+};
+
+result<double> get_exchange_rate( currency_type from, currency_type to );
+
+result<double> convert( double amount, currency_type from, currency_type to )
+{
+    return get_exchange_rate( from, to ) & [&](double rate){ return rate * amount; };
+}
+```
+
+```
+template<class T, class E, class F, class R = ...> R operator&( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator&( result<T, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the error in `r`, or if `r` contains a value, another `result` obtained
+by invoking the function `f` on the value in `r`.
++
+Let `R` be the type of `f(*r)`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `f(*r)`.
+  - Otherwise, returns `r.error()`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result` and `E` is convertible to `R::error_type`.
+Example: ::
++
+```
+struct JsonValue
+{
+    result<JsonValue const&> at( std::size_t i ) const noexcept;
+    result<JsonValue const&> at( std::string_view key ) const noexcept;
+    template<class T> result<T> to_number() const noexcept;
+};
+
+namespace helpers
+{
+
+inline auto at( std::size_t i ) {
+    return [=](JsonValue const& jv){ return jv.at( i ); }; }
+
+inline auto at( std::string_view key ) {
+    return [=](JsonValue const& jv){ return jv.at( key ); }; }
+
+template<class T> inline auto to_number() {
+    return [](JsonValue const& jv){ return jv.to_number<T>(); }; }
+
+} // namespace helpers
+
+int get_port( JsonValue const& config, int def )
+{
+    using namespace helpers;
+    return config.at( "servers" ) & at( 0 ) & at( "port" ) & to_number<int>() | def;
+}
+```
+
+#### operator&=
+
+```
+template<class T, class E, class F, class U = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
+```
+[none]
+* {blank}
++
+If `r` contains a value, replaces it with the result of invoking the function `f` on the value in `r`.
++
+Let `U` be the type of `f(*r)`.
++
+Effects: :: If `r.has_value()` is `true`, assigns `f(*std::move(r))` to `r`.
+Returns: :: `r`.
+Remarks: ::
+  Only enabled when `U` is not an instance of `result` and is convertible to `T`.
+
+```
+template<class T, class E, class F, class R = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
+```
+[none]
+* {blank}
++
+If `r` contains a value, replaces `r` with the result of invoking the function `f` on the value in `r`.
++
+Let `R` be the type of `f(*r)`.
++
+Effects: :: If `r.has_value()` is `true`, assigns `f(*std::move(r))` to `r`.
+Returns: :: `r`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result` and is convertible to `result<T, E>`.
+Example: ::
++
+```
+struct JsonValue
+{
+    result<JsonValue const&> at( std::string_view key ) const noexcept;
+};
+
+namespace helpers
+{
+
+inline auto at( std::string_view key ) {
+    return [=](JsonValue const& jv){ return jv.at( key ); }; }
+
+} // namespace helpers
+
+result<JsonValue const&> at_path( JsonValue const& jv,
+    std::initializer_list<std::string_view> path )
+{
+    result<JsonValue const&> r( jv );
+
+    using namespace helpers;
+
+    for( auto key: path )
+    {
+        r &= at( key );
+    }
+
+    return r;
+}
+```
+
 ## <boost/system.hpp>
 
 This convenience header includes all the headers previously described.

include/boost/system/detail/requires_cxx11.hpp

@@ -14,7 +14,7 @@
     defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) || \
     defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR)
 
-BOOST_PRAGMA_MESSAGE("C++03 support was deprecated in Boost.System 1.82 and will be removed in Boost.System 1.84. Please open an issue in https://github.com/boostorg/system if you want it retained.")
+BOOST_PRAGMA_MESSAGE("C++03 support was deprecated in Boost.System 1.82 and will be removed in Boost.System 1.85.")
 
 #endif
 

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() )
@@ -538,6 +545,23 @@ public:
     {
     }
 
+    // converting
+    template<class E2, class En = typename std::enable_if<
+        std::is_convertible<E2, E>::value
+        >::type>
+    BOOST_CXX14_CONSTEXPR result( result<void, E2> const& r2 )
+        noexcept(
+            std::is_nothrow_constructible<E, E2>::value &&
+            std::is_nothrow_default_constructible<E2>::value &&
+            std::is_nothrow_copy_constructible<E2>::value )
+        : v_( in_place_error, r2.error() )
+    {
+        if( r2 )
+        {
+            this->emplace();
+        }
+    }
+
     // queries
 
     constexpr bool has_value() const noexcept
@@ -635,6 +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() )
@@ -727,7 +758,8 @@ public:
 
     // tagged, value
     template<class A, class En = typename std::enable_if<
-        std::is_constructible<U&, A>::value
+        std::is_constructible<U&, A>::value &&
+        !detail::reference_to_temporary<U, A>::value
         >::type>
     constexpr result( in_place_value_t, A&& a )
         noexcept( std::is_nothrow_constructible<U&, A>::value )
@@ -867,6 +899,283 @@ 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
+{
+
+// is_value_convertible_to
+
+template<class T, class U> struct is_value_convertible_to: std::is_convertible<T, U>
+{
+};
+
+template<class T, class U> struct is_value_convertible_to<T, U&>:
+    std::integral_constant<bool,
+        std::is_lvalue_reference<T>::value &&
+        std::is_convertible<typename std::remove_reference<T>::type*, U*>::value>
+{
+};
+
+// is_result
+
+template<class T> struct is_result: std::false_type {};
+template<class T, class E> struct is_result< result<T, E> >: std::true_type {};
+
+} // namespace detail
+
+// result | value
+
+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 )
+{
+    if( r )
+    {
+        return *r;
+    }
+    else
+    {
+        return std::forward<U>( 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 )
+{
+    if( r )
+    {
+        return *std::move( r );
+    }
+    else
+    {
+        return std::forward<U>( u );
+    }
+}
+
+// result | nullary-returning-value
+
+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 )
+{
+    if( r )
+    {
+        return *r;
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+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 )
+{
+    if( r )
+    {
+        return *std::move( r );
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+// result | nullary-returning-result
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<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 )
+{
+    if( r )
+    {
+        return *r;
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<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 )
+{
+    if( r )
+    {
+        return *std::move( r );
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<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 )
+{
+    if( r )
+    {
+        return {};
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<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 )
+{
+    if( r )
+    {
+        return {};
+    }
+    else
+    {
+        return std::forward<F>( 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 )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *r );
+    }
+}
+
+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 )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *std::move( r ) );
+    }
+}
+
+// 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.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *r );
+    }
+}
+
+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.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *std::move( r ) );
+    }
+}
+
+// operator&=
+
+// result &= unary-returning-value
+
+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<detail::is_value_convertible_to<U, T>::value>::type
+>
+result<T, E>& operator&=( result<T, E>& r, F&& f )
+{
+    if( r )
+    {
+        r = std::forward<F>( f )( *std::move( r ) );
+    }
+
+    return r;
+}
+
+// result &= unary-returning-result
+
+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<detail::is_value_convertible_to<typename U::value_type, T>::value>::type,
+    class En3 = typename std::enable_if<std::is_convertible<typename U::error_type, E>::value>::type
+>
+result<T, E>& operator&=( result<T, E>& r, F&& f )
+{
+    if( r )
+    {
+        r = std::forward<F>( f )( *std::move( r ) );
+    }
+
+    return r;
+}
+
 } // namespace system
 } // namespace boost
 

test/CMakeLists.txt

@@ -167,3 +167,13 @@ boost_test(TYPE run SOURCES result_error_move.cpp)
 boost_test(TYPE run SOURCES result_value_construct6.cpp)
 boost_test(TYPE run SOURCES result_value_construct7.cpp)
 boost_test(TYPE run SOURCES result_error_construct5.cpp)
+boost_test(TYPE run SOURCES result_or_value.cpp)
+boost_test(TYPE compile-fail SOURCES result_or_value_fail.cpp)
+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_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

@@ -197,3 +197,13 @@ run result_error_move.cpp : : : $(CPP11) ;
 run result_value_construct6.cpp : : : $(CPP11) ;
 run result_value_construct7.cpp : : : $(CPP11) ;
 run result_error_construct5.cpp : : : $(CPP11) ;
+run result_or_value.cpp : : : $(CPP11) ;
+compile-fail result_or_value_fail.cpp : $(CPP11) ;
+compile-fail result_or_value_fail2.cpp : $(CPP11) ;
+run result_or_fn0v.cpp : : : $(CPP11) ;
+run result_or_fn0r.cpp : : : $(CPP11) ;
+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_and_eq_fn1r.cpp

@@ -0,0 +1,126 @@
+// 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&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+result<int, E> fi( int x )
+{
+    return 2 * x + 1;
+}
+
+result<int, E2> fi2( int )
+{
+    return E2();
+}
+
+result<X, E> fy( Y y )
+{
+    return X{ 2 * y.v_ + 1 };
+}
+
+result<Y, E2> fy2( Y )
+{
+    return E2();
+}
+
+result<int&, E> fri( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+result<int&, E2> fri2( int& )
+{
+    return E2();
+}
+
+int main()
+{
+    {
+        result<int, E2> r( 1 );
+
+        r &= fi;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 3 );
+
+        r &= fi2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fi;
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<Y, E2> r( in_place_value, 1 );
+
+        r &= fy;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 3 );
+
+        r &= fy2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fy;
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E2> r( x1 );
+
+        r &= fri;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &*fri( x1 ) );
+
+        r &= fri2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fri;
+        BOOST_TEST( r.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_and_eq_fn1v.cpp

@@ -0,0 +1,114 @@
+// 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&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+int f( int x )
+{
+    return x * 2 + 1;
+}
+
+X g( Y y )
+{
+    return X{ y.v_ * 2 + 1 };
+}
+
+int& h( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        r &= f;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 3 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        r &= f;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<Y> r( in_place_value, 1 );
+
+        r &= g;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 3 );
+    }
+
+    {
+        result<Y, E> r( in_place_error );
+
+        r &= g;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&> r( x1 );
+
+        r &= h;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &h( x1 ) );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        r &= h;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_and_fn1r.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();
+}

test/result_and_fn1v.cpp

@@ -0,0 +1,158 @@
+// 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
+{
+};
+
+int f( int x )
+{
+    return x * 2 + 1;
+}
+
+X g( Y y )
+{
+    return X{ y.v_ * 2 + 1 };
+}
+
+int& h( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+        result<int> r2 = r & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int> const r( 1 );
+        result<int> r2 = r & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int> r2 = result<int>( 1 ) & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+        result<int, E> r2 = r & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+        result<int, E> r2 = r & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E> r2 = result<int, E>( in_place_error ) & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X> r2 = result<Y>( in_place_value, 1 ) & g;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2->v_, 3 );
+    }
+
+    {
+        result<X, E> r2 = result<Y, E>( in_place_error ) & g;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        result<int&> r2 = r & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        result<int&> r2 = r & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r2 = result<int&>( x1 ) & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        result<int&, E> r2 = r & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        result<int&, E> r2 = r & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E> r2 = result<int&, E>( in_place_error ) & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_convert_construct.cpp

@@ -183,6 +183,67 @@ int main()
 
     //
 
+    {
+        result<void, int> r;
+        result<void, X> r2 = r;
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> const r;
+        result<void, X> r2 = r;
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, X> r2 = result<void, int>();
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> r( 5 );
+        result<void, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(5) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> const r( 6 );
+        result<void, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(6) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    {
+        result<void, X> r2 = result<void, int>( 7 );
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(7) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
     {
         int x = 5;
 
@@ -225,6 +286,9 @@ int main()
         BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, void*>, result<int, int>>));
         BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<int, int>, result<int, void*>>));
 
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<void, void*>, result<void, int>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<void, int>, result<void, void*>>));
+
         BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int const&>, result<int&>>));
         BOOST_TEST_TRAIT_TRUE((std::is_convertible<result<int&>, result<int const&>>));
 

test/result_default_construct.cpp

@@ -28,6 +28,24 @@ int main()
         BOOST_TEST_EQ( r.value(), 0 );
     }
 
+    {
+        result<int> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        result<int> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
     {
         result<X> r;
 
@@ -35,6 +53,20 @@ int main()
         BOOST_TEST( !r.has_error() );
     }
 
+    {
+        result<X> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<X> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
     {
         result<void> r;
 
@@ -42,6 +74,20 @@ int main()
         BOOST_TEST( !r.has_error() );
     }
 
+    {
+        result<void> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<void> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
     {
         BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<int>>));
         BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<int, int>>));

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();
+}

test/result_or_fn0r.cpp

@@ -0,0 +1,359 @@
+// 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
+{
+};
+
+result<int, E> fi()
+{
+    return 2;
+}
+
+result<int, E> fi2()
+{
+    return E();
+}
+
+result<Y, E> fy()
+{
+    return Y{ 2 };
+}
+
+result<Y, E> fy2()
+{
+    return E();
+}
+
+result<int&, E> fri()
+{
+    static int x = 2;
+    return x;
+}
+
+result<int&, E> fri2()
+{
+    return E();
+}
+
+result<void, E> fv()
+{
+    return {};
+}
+
+result<void, E> fv2()
+{
+    return E();
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | fi | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> r( 1 );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> r( in_place_error );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int> const r( in_place_error );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        int x = result<int>( in_place_error ) | fi | 3;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int> r( in_place_error );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 3 );
+    }
+
+    {
+        result<int> const r( in_place_error );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 3 );
+    }
+
+    {
+        int x = result<int>( in_place_error ) | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 3 );
+    }
+
+    {
+        Y y = result<X>( X{1} ) | fy | X{3};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<X>( X{1} ) | fy2 | X{3};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<X, E>( in_place_error ) | fy | X{3};
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        Y y = result<X, E>( in_place_error ) | fy2 | Y{3};
+
+        BOOST_TEST_EQ( y.v_, 3 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> r( x1 );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> const r( x1 );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        int& x = result<int&>( x1 ) | fri | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> r( x1 );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> const r( x1 );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        int& x = result<int&>( x1 ) | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> r( in_place_error );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &*fri() );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &*fri() );
+    }
+
+    {
+        int x3 = 3;
+
+        int& x = result<int&, E>( in_place_error ) | fri | x3;
+
+        BOOST_TEST_EQ( &x, &*fri() );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> r( in_place_error );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x3 );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x3 );
+    }
+
+    {
+        int x3 = 3;
+
+        int& x = result<int&, E>( in_place_error ) | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x3 );
+    }
+
+    {
+        result<void> r;
+        result<void, E> r2 = r | fv;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void> r;
+        result<void, E> r2 = r | fv2;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void> r( in_place_error );
+        result<void, E> r2 = r | fv;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void> r( in_place_error );
+        result<void, E> r2 = r | fv2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E> r2 = result<void>() | fv;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void, E> r2 = result<void>() | fv2;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void, E> r2 = result<void>( in_place_error ) | fv;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void, E> r2 = result<void>( in_place_error ) | fv2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_or_fn0v.cpp

@@ -0,0 +1,162 @@
+// 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
+{
+};
+
+int f()
+{
+    return 2;
+}
+
+X g()
+{
+    return { 2 };
+}
+
+int& h()
+{
+    static int x = 2;
+    return x;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | f;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        int x = result<int, E>( in_place_error ) | f;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        Y y = result<Y>( in_place_value, 1 ) | g;
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<Y, E>( in_place_error ) | g;
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        int& x = result<int&>( x1 ) | h;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &h() );
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &h() );
+    }
+
+    {
+        int& x = result<int&, E>( in_place_error ) | h;
+
+        BOOST_TEST_EQ( &x, &h() );
+    }
+
+    return boost::report_errors();
+}

test/result_or_value.cpp

@@ -0,0 +1,167 @@
+// 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
+{
+};
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | 2;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        int x = result<int, E>( in_place_error ) | 2;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        Y y = result<Y>( in_place_value, 1 ) | Y{2};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<Y, E>( in_place_error ) | Y{2};
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        Y y = result<Y>( in_place_value, 1 ) | X{2};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<Y, E>( in_place_error ) | X{2};
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r( x1 );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> const r( x1 );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        int& x = result<int&>( x1 ) | x2;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x2 = 2;
+
+        result<int&, E> r( in_place_error );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x2 );
+    }
+
+    {
+        int x2 = 2;
+
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x2 );
+    }
+
+    {
+        int x2 = 2;
+
+        int& x = result<int&, E>( in_place_error ) | x2;
+
+        BOOST_TEST_EQ( &x, &x2 );
+    }
+
+    return boost::report_errors();
+}

test/result_or_value_fail.cpp

@@ -0,0 +1,14 @@
+// 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>
+
+using namespace boost::system;
+
+int main()
+{
+    int x = 1;
+    result<int const&> r( x );
+    r | 2;
+}

test/result_or_value_fail2.cpp

@@ -0,0 +1,13 @@
+// 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>
+
+using namespace boost::system;
+
+int main()
+{
+    int x = 1;
+    result<int const&>( x ) | 2;
+}

test/result_value_construct2.cpp

@@ -69,6 +69,11 @@ result<std::vector<int>> fv2()
     return {{ 1, 2 }};
 }
 
+result<void> fw0()
+{
+    return {};
+}
+
 int main()
 {
     {
@@ -148,5 +153,12 @@ int main()
         BOOST_TEST_EQ( r->at(1), 2 );
     }
 
+    {
+        result<void> r = fw0();
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
     return boost::report_errors();
 }