From 16731d26899e9f551f9f7691d14944e5a34ec2ec Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Wed, 3 Jan 2018 19:26:11 +0200
Subject: [PATCH] Make boost::tuple tuple-like to support structured bindings

---
 include/boost/tuple/detail/tuple_basic.hpp | 21 +++---
 include/boost/tuple/tuple.hpp              | 39 +++++++++++
 test/Jamfile                               |  3 +
 test/std_tuple_element.cpp                 | 56 ++++++++++++++++
 test/std_tuple_size.cpp                    | 61 +++++++++++++++++
 test/structured_bindings.cpp               | 77 ++++++++++++++++++++++
 6 files changed, 247 insertions(+), 10 deletions(-)
 create mode 100644 test/std_tuple_element.cpp
 create mode 100644 test/std_tuple_size.cpp
 create mode 100644 test/structured_bindings.cpp

diff --git a/include/boost/tuple/detail/tuple_basic.hpp b/include/boost/tuple/detail/tuple_basic.hpp
index 879f0e9..4ea13ef 100644
--- a/include/boost/tuple/detail/tuple_basic.hpp
+++ b/include/boost/tuple/detail/tuple_basic.hpp
@@ -37,6 +37,7 @@
 
 #include <boost/type_traits/cv_traits.hpp>
 #include <boost/type_traits/function_traits.hpp>
+#include <boost/type_traits/integral_constant.hpp>
 #include <boost/utility/swap.hpp>
 
 #include <boost/detail/workaround.hpp> // needed for BOOST_WORKAROUND
@@ -420,28 +421,28 @@ struct cons<HT, null_type> {
 // templates for finding out the length of the tuple -------------------
 
 template<class T>
-struct length  {
-  BOOST_STATIC_CONSTANT(int, value = 1 + length<typename T::tail_type>::value);
+struct length: boost::integral_constant<int, 1 + length<typename T::tail_type>::value>
+{
 };
 
 template<>
-struct length<tuple<> > {
-  BOOST_STATIC_CONSTANT(int, value = 0);
+struct length<tuple<> >: boost::integral_constant<int, 0>
+{
 };
 
 template<>
-struct length<tuple<> const> {
-  BOOST_STATIC_CONSTANT(int, value = 0);
+struct length<tuple<> const>: boost::integral_constant<int, 0>
+{
 };
 
 template<>
-struct length<null_type> {
-  BOOST_STATIC_CONSTANT(int, value = 0);
+struct length<null_type>: boost::integral_constant<int, 0>
+{
 };
 
 template<>
-struct length<null_type const> {
-  BOOST_STATIC_CONSTANT(int, value = 0);
+struct length<null_type const>: boost::integral_constant<int, 0>
+{
 };
 
 namespace detail {
diff --git a/include/boost/tuple/tuple.hpp b/include/boost/tuple/tuple.hpp
index d71e7df..4f2f8ac 100644
--- a/include/boost/tuple/tuple.hpp
+++ b/include/boost/tuple/tuple.hpp
@@ -63,5 +63,44 @@ get(const tuples::cons<HT, TT>& c) {
 
 } // end namespace boost
 
+#if !defined(BOOST_NO_CXX11_HDR_TUPLE)
+
+#include <tuple>
+#include <cstddef>
+
+namespace std
+{
+
+// std::tuple_size
+
+template<class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10>
+    struct tuple_size< boost::tuples::tuple<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> >:
+        boost::tuples::length< boost::tuples::tuple<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> >
+{
+};
+
+template<class H, class T> struct tuple_size< boost::tuples::cons<H, T> >: boost::tuples::length< boost::tuples::cons<H, T> >
+{
+};
+
+template<> struct tuple_size< boost::tuples::null_type >: boost::tuples::length< boost::tuples::null_type >
+{
+};
+
+// std::tuple_element
+
+template<std::size_t I, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10>
+    struct tuple_element< I, boost::tuples::tuple<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> >:
+        boost::tuples::element< I, boost::tuples::tuple<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> >
+{
+};
+
+template<std::size_t I, class H, class T> struct tuple_element< I, boost::tuples::cons<H, T> >: boost::tuples::element< I, boost::tuples::cons<H, T> >
+{
+};
+
+} // namespace std
+
+#endif // !defined(BOOST_NO_CXX11_HDR_TUPLE)
 
 #endif // BOOST_TUPLE_HPP
diff --git a/test/Jamfile b/test/Jamfile
index af6c22c..7159dce 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -5,4 +5,7 @@ test-suite tuple :
     [ run tuple_test_bench.cpp ]
     [ run io_test.cpp ]
     [ run another_tuple_test_bench.cpp ]
+    [ run std_tuple_size.cpp ]
+    [ run std_tuple_element.cpp ]
+    [ run structured_bindings.cpp ]
     ;
diff --git a/test/std_tuple_element.cpp b/test/std_tuple_element.cpp
new file mode 100644
index 0000000..762d1fa
--- /dev/null
+++ b/test/std_tuple_element.cpp
@@ -0,0 +1,56 @@
+// Copyright 2017 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+
+#include <boost/tuple/tuple.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <boost/type_traits/is_same.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX11_HDR_TUPLE)
+
+BOOST_PRAGMA_MESSAGE("Skipping std::tuple_element tests for lack of <tuple>")
+int main() {}
+
+#else
+
+#include <tuple>
+
+template<class Tp, std::size_t I, class E> void test()
+{
+    BOOST_TEST_TRAIT_TRUE((boost::is_same<typename std::tuple_element<I, Tp>::type, E>));
+
+    typedef typename Tp::inherited Tp2;
+    BOOST_TEST_TRAIT_TRUE((boost::is_same<typename std::tuple_element<I, Tp2>::type, E>));
+}
+
+template<int> struct X
+{
+};
+
+int main()
+{
+    test<boost::tuple<X<0> const>, 0, X<0> const>();
+
+    test<boost::tuple<X<0> const, X<1> const>, 0, X<0> const>();
+    test<boost::tuple<X<0> const, X<1> const>, 1, X<1> const>();
+
+    test<boost::tuple<X<0> const, X<1> const, X<2> const>, 0, X<0> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const>, 1, X<1> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const>, 2, X<2> const>();
+
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const>, 0, X<0> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const>, 1, X<1> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const>, 2, X<2> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const>, 3, X<3> const>();
+
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const, X<4> const>, 0, X<0> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const, X<4> const>, 1, X<1> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const, X<4> const>, 2, X<2> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const, X<4> const>, 3, X<3> const>();
+    test<boost::tuple<X<0> const, X<1> const, X<2> const, X<3> const, X<4> const>, 4, X<4> const>();
+
+    return boost::report_errors();
+}
+
+#endif
diff --git a/test/std_tuple_size.cpp b/test/std_tuple_size.cpp
new file mode 100644
index 0000000..5525f63
--- /dev/null
+++ b/test/std_tuple_size.cpp
@@ -0,0 +1,61 @@
+// Copyright 2017 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+
+#include <boost/tuple/tuple.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX11_HDR_TUPLE)
+
+BOOST_PRAGMA_MESSAGE("Skipping std::tuple_size tests for lack of <tuple>")
+int main() {}
+
+#else
+
+#include <tuple>
+
+template<class Tp> void test( std::size_t x )
+{
+    BOOST_TEST_EQ( std::tuple_size< Tp >::value, x );
+    BOOST_TEST_EQ( std::tuple_size< typename Tp::inherited >::value, x );
+}
+
+struct V
+{
+};
+
+int main()
+{
+    test< boost::tuple<> >( 0 );
+    test< boost::tuple<V> >( 1 );
+    test< boost::tuple<V, V> >( 2 );
+    test< boost::tuple<V, V, V> >( 3 );
+    test< boost::tuple<V, V, V, V> >( 4 );
+    test< boost::tuple<V, V, V, V, V> >( 5 );
+    test< boost::tuple<V, V, V, V, V, V> >( 6 );
+    test< boost::tuple<V, V, V, V, V, V, V> >( 7 );
+    test< boost::tuple<V, V, V, V, V, V, V, V> >( 8 );
+    test< boost::tuple<V, V, V, V, V, V, V, V, V> >( 9 );
+    test< boost::tuple<V, V, V, V, V, V, V, V, V, V> >( 10 );
+
+#if !defined(BOOST_NO_CXX11_DECLTYPE)
+
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple())>::value, 0 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1))>::value, 1 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2))>::value, 2 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3))>::value, 3 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3, 4))>::value, 4 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3, 4, 5))>::value, 5 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3, 4, 5, 6))>::value, 6 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3, 4, 5, 6, 7))>::value, 7 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3, 4, 5, 6, 7, 8))>::value, 8 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3, 4, 5, 6, 7, 8, 9))>::value, 9 );
+    BOOST_TEST_EQ( std::tuple_size<decltype(boost::make_tuple(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))>::value, 10 );
+
+#endif
+
+    return boost::report_errors();
+}
+
+#endif
diff --git a/test/structured_bindings.cpp b/test/structured_bindings.cpp
new file mode 100644
index 0000000..432ba0a
--- /dev/null
+++ b/test/structured_bindings.cpp
@@ -0,0 +1,77 @@
+// Copyright 2017 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+
+#include <boost/tuple/tuple.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX17_STRUCTURED_BINDINGS)
+
+BOOST_PRAGMA_MESSAGE("Skipping structured bindings test, not supported")
+int main() {}
+
+#else
+
+int main()
+{
+    // make_tuple
+
+    {
+        auto [x1] = boost::make_tuple( 1 );
+        BOOST_TEST_EQ( x1, 1 );
+    }
+
+    {
+        auto [x1, x2] = boost::make_tuple( 1, 2 );
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+    }
+
+    {
+        auto [x1, x2, x3] = boost::make_tuple( 1, 2, 3 );
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+        BOOST_TEST_EQ( x3, 3 );
+    }
+
+    {
+        auto [x1, x2, x3, x4] = boost::make_tuple( 1, 2, 3, 4 );
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+        BOOST_TEST_EQ( x3, 3 );
+        BOOST_TEST_EQ( x4, 4 );
+    }
+
+    // tuple
+
+    {
+        auto [x1] = boost::tuple<int>( 1 );
+        BOOST_TEST_EQ( x1, 1 );
+    }
+
+    {
+        auto [x1, x2] = boost::tuple<int, int>( 1, 2 );
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+    }
+
+    {
+        auto [x1, x2, x3] = boost::tuple<int, int, int>( 1, 2, 3 );
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+        BOOST_TEST_EQ( x3, 3 );
+    }
+
+    {
+        auto [x1, x2, x3, x4] = boost::tuple<int, int, int, int>( 1, 2, 3, 4 );
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+        BOOST_TEST_EQ( x3, 3 );
+        BOOST_TEST_EQ( x4, 4 );
+    }
+
+    return boost::report_errors();
+}
+
+#endif