Fix missing include for unique_ptr. (#125)

Always define is_implicitly_reflectable

README.md

@@ -45,6 +45,8 @@ Outputs:
 Edgar Allan Poe was born in 1809
 ```
 
+[Run the above sample](https://godbolt.org/z/PfYsWKb7v)
+
 
 ### Motivating Example #1
 ```c++

doc/Jamfile.v2

@@ -34,7 +34,9 @@ local doxygen_params =
             \"podops=\\b See \\b Also : \\xmlonly<link linkend='boost_pfr.tutorial.three_ways_of_getting_operators'>\\endxmlonly 'Three ways of getting operators' \\xmlonly</link>\\endxmlonly\" \\
             \"customio=\\b See \\b Also : \\xmlonly<link linkend='boost_pfr.tutorial.custom_printing_of_aggregates'>\\endxmlonly 'Custom printing of aggregates' \\xmlonly</link>\\endxmlonly for info on how to implement your own manipulator with custom format.\" \\
             \"aggregate=\\xmlonly<link linkend='boost_pfr.limitations_and_configuration'>\\endxmlonly simple aggregate \\xmlonly</link>\\endxmlonly\" \\
-            \"BOOST_PFR_DOXYGEN_INVOKED\" \\
+        "
+        <doxygen:param>"PREDEFINED= \\
+            \"BOOST_PFR_DOXYGEN_INVOKED=1\" \\
         "
     ;
 
@@ -52,7 +54,7 @@ boostbook pfr-doc
         pfr.qbk
     :
         <dependency>autodoc_pfr
-        <xsl:param>boost.root=https://www.boost.org/doc/libs/1_72_0
+        <xsl:param>boost.root=https://www.boost.org/doc/libs/1_81_0
         #<xsl:param>boost.root=../../../.
         <xml:param>html.stylesheet=../../../../doc/src/boostbook.css
     ;

doc/pfr.qbk

@@ -1,6 +1,6 @@
 [library Boost.PFR
     [quickbook 1.6]
-    [version 2.0]
+    [version 2.1]
     [copyright 2016-2023 Antony Polukhin]
     [category Language Features Emulation]
     [license
@@ -17,6 +17,7 @@ Boost.PFR is a C++14 library for a very basic reflection. It gives you access to
 [import ../example/motivating_example0.cpp]
 [pfr_motivating_example]
 
+Experiment with the sample [@https://godbolt.org/z/PfYsWKb7v online].
 See [link boost_pfr.limitations_and_configuration [*limitations]].
 
 
@@ -42,20 +43,20 @@ user_info retrieve_friend(std::string_view name) {
         name
     );
 
-    ////////////////////////////////////////////////////////////////////////////////
+    /////////////////////////////////////////////////////////////////////////////
     user_info info {
         std::move(std::get<0>(info_tuple)),
         std::move(std::get<1>(info_tuple)),
         std::move(std::get<2>(info_tuple)),
         std::move(std::get<3>(info_tuple)),
     }
-    ////////////////////////////////////////////////////////////////////////////////
+    /////////////////////////////////////////////////////////////////////////////
 
     auto friend_info = ask_user_for_friend(std::move(info));
 
     db::insert(
         "INSERT INTO user_infos(id, name, email, login) VALUES ($0, $1, $2, $3)",
-        friend_info.id,    /////////////////////////////////////////////////////////
+        friend_info.id,    //////////////////////////////////////////////////////
         friend_info.name,  // Users are forced to enumerate fields because your
         friend_info.email, // library can not iterate over the fields of a user
         friend_info.login  // provided structure
@@ -80,20 +81,20 @@ user_info retrieve_friend(std::string_view name) {
         name
     );
 
-    ////////////////// No boilerplate code to move data around /////////////////////
+    ////////////////// No boilerplate code to move data around //////////////////
 
 
 
 
 
 
-    ////////////////////////////////////////////////////////////////////////////////
+    /////////////////////////////////////////////////////////////////////////////
 
     auto friend_info = ask_user_for_friend(std::move(info));
 
     db::insert(
         "INSERT INTO user_infos(id, name, email, login) VALUES ($0, $1, $2, $3)",
-        friend_info     ////////////////////////////////////////////////////////////
+        friend_info     /////////////////////////////////////////////////////////
                         // Boost.PFR allows you to iterate over all the fields
                         // of a user provided structure
                         //
@@ -119,7 +120,7 @@ struct user_info {
     std::string name, email, login;
 };
 
-/// Customizations via hand-written code or macro like BOOST_FUSION_ADAPT_STRUCT ///
+/// Customizations via hand-written code ////////////////////////////////////////
 auto db_api_tie(user_info& ui) noexcept {
     return std::tie(ui.id, ui.name, ui.email, ui.login);
 }
@@ -127,7 +128,7 @@ auto db_api_tie(user_info& ui) noexcept {
 auto db_api_tie(const user_info& ui) noexcept {
     return std::tie(ui.id, ui.name, ui.email, ui.login);
 }
-////////////////////////////////////////////////////////////////////////////////////
+/////////////////////////////////////////////////////////////////////////////////
 ```
 ][
 ```
@@ -138,7 +139,7 @@ struct user_info {
     std::string name, email, login;
 };
 
-//////// With Boost.PFR there's no need in hand written customizations /////////////
+//////// With Boost.PFR there's no need in hand written customizations //////////
 
 
 
@@ -146,14 +147,29 @@ struct user_info {
 
 
 
-////////////////////////////////////////////////////////////////////////////////////
+/////////////////////////////////////////////////////////////////////////////////
 ```
 ]]
 ]
 
 
+Imagine that you are writing a serialization library. Serialization of user
+provided structures (and nested structures) with Boost.PFR it is just as simple as:
+
+```
+void Write(Writer& writer, int value);
+void Write(Writer& writer, std::string_view value);
+
+template <typename T>
+std::enable_if_t<std::is_aggregate_v<T>> Write(Writer& writer, const T& value) {
+  boost::pfr::for_each_field(
+      value, [&writer](const auto& field) { Write(writer, field); });
+}
+```
+
 With Boost.PFR the code is shorter, more readable and more pleasant to write.
 
+[note All the above examples were inspired by the Boost.PFR usage in [@https://github.com/userver-framework/userver 🐙 userver framework].]
 
 
 [h2 Out of the box functionality ]
@@ -164,7 +180,7 @@ Boost.PFR adds the following out-of-the-box functionality for aggregate initiali
 * heterogeneous comparators
 * hash
 * IO streaming
-* access to members by index
+* access to members by index or type
 * member type retrieval
 * methods for cooperation with `std::tuple`
 * methods to visit each field of the structure

example/quick_examples.cpp

@@ -91,7 +91,7 @@ void test_examples() {
 
   {
 //[pfr_quick_examples_get
-    // Get field by index and assign new value to that field
+    // Get field by index/type and assign new value to that field
 
     struct sample {
         char c;
@@ -100,8 +100,9 @@ void test_examples() {
 
     sample var{};
     boost::pfr::get<1>(var) = 42.01f;
+    boost::pfr::get<char>(var) = 'A';
 
-    std::cout << var.f; // Outputs: 42.01
+    std::cout << var.c << var.f; // Outputs: A 42.01
 //]
   }
 

include/boost/pfr/core.hpp

@@ -30,20 +30,25 @@
 namespace boost { namespace pfr {
 
 /// \brief Returns reference or const reference to a field with index `I` in \aggregate `val`.
+/// Overload taking the type `U` returns reference or const reference to a field
+/// with provided type `U` in \aggregate `val` if there's only one field of such type in `val`.
 ///
 /// \b Example:
 /// \code
 ///     struct my_struct { int i, short s; };
 ///     my_struct s {10, 11};
+///
 ///     assert(boost::pfr::get<0>(s) == 10);
 ///     boost::pfr::get<1>(s) = 0;
+///
+///     assert(boost::pfr::get<int>(s) == 10);
+///     boost::pfr::get<short>(s) = 11;
 /// \endcode
 template <std::size_t I, class T>
 constexpr decltype(auto) get(const T& val) noexcept {
     return detail::sequence_tuple::get<I>( detail::tie_as_tuple(val) );
 }
 
-
 /// \overload get
 template <std::size_t I, class T>
 constexpr decltype(auto) get(T& val
@@ -71,6 +76,40 @@ constexpr auto get(T&& val, std::enable_if_t< std::is_rvalue_reference<T&&>::val
 }
 
 
+/// \overload get
+template <class U, class T>
+constexpr const U& get(const T& val) noexcept {
+    return detail::sequence_tuple::get_by_type_impl<const U&>( detail::tie_as_tuple(val) );
+}
+
+
+/// \overload get
+template <class U, class T>
+constexpr U& get(T& val
+#if !BOOST_PFR_USE_CPP17
+    , std::enable_if_t<std::is_assignable<T, T>::value>* = nullptr
+#endif
+) noexcept {
+    return detail::sequence_tuple::get_by_type_impl<U&>( detail::tie_as_tuple(val) );
+}
+
+#if !BOOST_PFR_USE_CPP17
+/// \overload get
+template <class U, class T>
+constexpr U& get(T&, std::enable_if_t<!std::is_assignable<T, T>::value>* = nullptr) noexcept {
+    static_assert(sizeof(T) && false, "====================> Boost.PFR: Calling boost::pfr::get on non const non assignable type is allowed only in C++17");
+    return 0;
+}
+#endif
+
+
+/// \overload get
+template <class U, class T>
+constexpr U&& get(T&& val, std::enable_if_t< std::is_rvalue_reference<T&&>::value>* = nullptr) noexcept {
+    return std::move(detail::sequence_tuple::get_by_type_impl<U&>( detail::tie_as_tuple(val) ));
+}
+
+
 /// \brief `tuple_element` has a member typedef `type` that returns the type of a field with index I in \aggregate T.
 ///
 /// \b Example:

include/boost/pfr/detail/core14_classic.hpp

@@ -53,7 +53,7 @@ namespace typeid_conversions {
 #ifdef _MSC_VER
 #   pragma warning( push )
     // '<<': check operator precedence for possible error; use parentheses to clarify precedence
-#   pragma warning( disable : 4554 ) 
+#   pragma warning( disable : 4554 )
 #endif
 
 constexpr std::size_t native_types_mask = 31;

include/boost/pfr/detail/core14_loophole.hpp

@@ -8,7 +8,7 @@
 // The Great Type Loophole (C++14)
 // Initial implementation by Alexandr Poltavsky, http://alexpolt.github.io
 //
-// Description: 
+// Description:
 //  The Great Type Loophole is a technique that allows to exchange type information with template
 //  instantiations. Basically you can assign and read type information during compile time.
 //  Here it is used to detect data members of a data type. I described it for the first time in

include/boost/pfr/detail/possible_reflectable.hpp

@@ -20,6 +20,8 @@ constexpr decltype(is_reflectable<T, WhatFor>::value) possible_reflectable(long)
     return is_reflectable<T, WhatFor>::value;
 }
 
+#if BOOST_PFR_ENABLE_IMPLICIT_REFLECTION
+
 template <class T, class WhatFor>
 constexpr bool possible_reflectable(int) noexcept {
 #   if  defined(__cpp_lib_is_aggregate)
@@ -30,6 +32,16 @@ constexpr bool possible_reflectable(int) noexcept {
 #   endif
 }
 
+#else
+
+template <class T, class WhatFor>
+constexpr bool possible_reflectable(int) noexcept {
+    // negative answer here won't change behaviour in PFR-dependent libraries(like Fusion)
+    return false;
+}
+
+#endif
+
 }}} // namespace boost::pfr::detail
 
 #endif // BOOST_PFR_DETAIL_POSSIBLE_REFLECTABLE_HPP

include/boost/pfr/detail/sequence_tuple.hpp

@@ -79,6 +79,45 @@ constexpr T&& get_impl(base_from_member<N, T>&& t) noexcept {
 }
 
 
+template <class T, std::size_t N>
+constexpr T& get_by_type_impl(base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr const T& get_by_type_impl(const base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr volatile T& get_by_type_impl(volatile base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr const volatile T& get_by_type_impl(const volatile base_from_member<N, T>& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn)
+    return t.value;
+}
+
+template <class T, std::size_t N>
+constexpr T&& get_by_type_impl(base_from_member<N, T>&& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn)
+    return std::forward<T>(t.value);
+}
+
+template <class T, std::size_t N>
+constexpr const T&& get_by_type_impl(const base_from_member<N, T>&& t) noexcept {
+    // NOLINTNEXTLINE(clang-analyzer-core.uninitialized.UndefReturn)
+    return std::forward<T>(t.value);
+}
+
+
+
+
 template <class ...Values>
 struct tuple: tuple_base<
     detail::index_sequence_for<Values...>,

include/boost/pfr/traits.hpp

@@ -19,8 +19,8 @@
 
 namespace boost { namespace pfr {
 
-/// Has a static const member variable `value` when it known that type T can or can't be reflected using Boost.PFR; otherwise, there is no member variable.
-/// Every user may(and in some difficult cases - should) specialize is_reflectable on his own.
+/// Has a static const member variable `value` when it is known that type T can or can't be reflected using Boost.PFR; otherwise, there is no member variable.
+/// Every user may (and in some difficult cases - should) specialize is_reflectable on his own.
 ///
 /// \b Example:
 /// \code
@@ -29,11 +29,9 @@ namespace boost { namespace pfr {
 ///         template<> struct is_reflectable<B, boost_fusion_tag> : std::false_type {};   // 'B' won't be interpreted as reflectable in only Boost Fusion
 ///     }}
 /// \endcode
-/// \note is_reflectable affects is_implicitly_reflectable, the decision made by is_reflectable has more priority than is_implicitly_reflectable,
-///       because is_reflectable is more sharp than is_implicitly_reflectable
-///
+/// \note is_reflectable affects is_implicitly_reflectable, the decision made by is_reflectable is used by is_implicitly_reflectable.
 template<class T, class WhatFor>
-struct is_reflectable { /*  do not has 'value' because value is unknown */ };
+struct is_reflectable { /*  does not have 'value' because value is unknown */ };
 
 // these specs can't be inherited from 'std::integral_constant< bool, boost::pfr::is_reflectable<T, WhatFor>::value >',
 // because it will break the sfinae-friendliness
@@ -46,17 +44,15 @@ struct is_reflectable<volatile T, WhatFor> : boost::pfr::is_reflectable<T, WhatF
 template<class T, class WhatFor>
 struct is_reflectable<const volatile T, WhatFor> : boost::pfr::is_reflectable<T, WhatFor> {};
 
-#if BOOST_PFR_ENABLE_IMPLICIT_REFLECTION
 /// Checks the input type for the potential to be reflected.
-/// Specialize is_reflectable if you are disagree with is_implicitly_reflectable's default decision.
+/// Specialize is_reflectable if you disagree with is_implicitly_reflectable's default decision.
 template<class T, class WhatFor>
 using is_implicitly_reflectable = std::integral_constant< bool, boost::pfr::detail::possible_reflectable<T, WhatFor>(1L) >;
 
 /// Checks the input type for the potential to be reflected.
-/// Specialize is_reflectable if you are disagree with is_implicitly_reflectable_v's default decision.
+/// Specialize is_reflectable if you disagree with is_implicitly_reflectable_v's default decision.
 template<class T, class WhatFor>
 constexpr bool is_implicitly_reflectable_v = is_implicitly_reflectable<T, WhatFor>::value;
-#endif
 
 }} // namespace boost::pfr
 

test/core/run/get_by_type.cpp

@@ -0,0 +1,67 @@
+// Copyright (c) 2020-2023 Antony Polukhin
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+
+#include <boost/pfr/core.hpp>
+
+#include <boost/core/lightweight_test.hpp>
+
+namespace testing {
+
+namespace {
+
+struct Aggregate {
+    int a;
+    const int b;
+    double c;
+    double d;
+    short e;
+};
+
+void test_get_by_type() {
+#if BOOST_PFR_USE_CPP17
+    Aggregate t{1, 2, 3.4, 5.6, 7};
+
+    BOOST_TEST_EQ(boost::pfr::get<int>(t), 1);
+    BOOST_TEST_EQ(boost::pfr::get<const int>(t), 2);
+    BOOST_TEST_EQ(boost::pfr::get<short>(t), 7);
+
+    boost::pfr::get<int>(t) = 11;
+    boost::pfr::get<short>(t) = 77;
+#endif
+}
+
+void test_const_get_by_type() {
+#if BOOST_PFR_USE_CPP17 || BOOST_PFR_USE_LOOPHOLE
+    const Aggregate t{1, 2, 3.4, 5.6, 7};
+    BOOST_TEST_EQ(boost::pfr::get<short>(t), 7);
+#endif
+}
+
+void test_get_by_type_pod() {
+    struct PodAggregate {
+      int i;
+      short s;
+    };
+
+    PodAggregate pod{1, 2};
+    BOOST_TEST_EQ(boost::pfr::get<int>(pod), 1);
+    BOOST_TEST_EQ(boost::pfr::get<short>(pod), 2);
+}
+
+} // anonymous namespace
+
+
+} // namespace testing
+
+int main() {
+    testing::test_get_by_type();
+    testing::test_const_get_by_type();
+    testing::test_get_by_type_pod();
+
+    return boost::report_errors();
+}
+
+

test/core/run/issue33.cpp

@@ -6,6 +6,7 @@
 // Test case for https://github.com/boostorg/pfr/issues/33
 
 #include <iostream>
+#include <memory>
 #include <vector>
 #include <boost/pfr.hpp>
 #include <boost/core/lightweight_test.hpp>