From 2cd4753a02634a9f15e23e87ca8c176f3e296f1f Mon Sep 17 00:00:00 2001
From: Glen Fernandes <glen.fernandes@gmail.com>
Date: Sat, 7 Jul 2018 23:13:03 -0400
Subject: [PATCH] Implement boost::exchange

---
 include/boost/core/exchange.hpp | 47 +++++++++++++++++++++
 test/Jamfile.v2                 |  3 ++
 test/exchange_move_test.cpp     | 73 +++++++++++++++++++++++++++++++++
 test/exchange_test.cpp          | 65 +++++++++++++++++++++++++++++
 4 files changed, 188 insertions(+)
 create mode 100644 include/boost/core/exchange.hpp
 create mode 100644 test/exchange_move_test.cpp
 create mode 100644 test/exchange_test.cpp

diff --git a/include/boost/core/exchange.hpp b/include/boost/core/exchange.hpp
new file mode 100644
index 0000000..c31f2af
--- /dev/null
+++ b/include/boost/core/exchange.hpp
@@ -0,0 +1,47 @@
+/*
+Copyright 2018 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#ifndef BOOST_CORE_EXCHANGE_HPP
+#define BOOST_CORE_EXCHANGE_HPP
+
+#include <boost/config.hpp>
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#include <utility>
+#endif
+
+namespace boost {
+
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+template<class T, class U = T>
+BOOST_CXX14_CONSTEXPR inline T exchange(T& t, U&& u)
+{
+    T v = std::move(t);
+    t = std::forward<U>(u);
+    return v;
+}
+#else
+namespace detail {
+
+template<class T>
+struct exchanger {
+    typedef T type;
+};
+
+} /* detail */
+
+template<class T>
+inline T exchange(T& t, const typename detail::exchanger<T>::type& u)
+{
+    T v = t;
+    t = u;
+    return v;
+}
+#endif
+
+} /* boost */
+
+#endif
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 66b96fc..ba801e6 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -121,5 +121,8 @@ run pointer_traits_rebind_test.cpp ;
 run pointer_traits_pointer_to_test.cpp ;
 run to_address_test.cpp ;
 
+run exchange_test.cpp ;
+run exchange_move_test.cpp ;
+
 use-project /boost/core/swap : ./swap ;
 build-project ./swap ;
diff --git a/test/exchange_move_test.cpp b/test/exchange_move_test.cpp
new file mode 100644
index 0000000..57255b8
--- /dev/null
+++ b/test/exchange_move_test.cpp
@@ -0,0 +1,73 @@
+/*
+Copyright 2018 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#include <boost/config.hpp>
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#include <boost/core/exchange.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+class C1 {
+public:
+    explicit C1(int i)
+        : i_(i) { }
+    C1(C1&& c)
+        : i_(c.i_) { }
+    C1& operator=(C1&& c) {
+        i_ = c.i_;
+        return *this;
+    }
+    int i() const {
+        return i_;
+    }
+private:
+    C1(const C1&);
+    C1& operator=(const C1&);
+    int i_;
+};
+
+void test1()
+{
+    C1 x(1);
+    BOOST_TEST(boost::exchange(x, C1(2)).i() == 1);
+    BOOST_TEST(x.i() == 2);
+}
+
+class C2 {
+public:
+    explicit C2(int i)
+        : i_(i) { }
+    operator C1() const {
+        return C1(i_);
+    }
+    int i() const {
+        return i_;
+    }
+private:
+    C2(const C2&);
+    C2& operator=(const C2&);
+    int i_;
+};
+
+void test2()
+{
+    C1 x(1);
+    BOOST_TEST(boost::exchange(x, C2(2)).i() == 1);
+    BOOST_TEST(x.i() == 2);
+}
+
+int main()
+{
+    test1();
+    test2();
+    return boost::report_errors();
+}
+#else
+int main()
+{
+    return 0;
+}
+#endif
diff --git a/test/exchange_test.cpp b/test/exchange_test.cpp
new file mode 100644
index 0000000..a370d11
--- /dev/null
+++ b/test/exchange_test.cpp
@@ -0,0 +1,65 @@
+/*
+Copyright 2018 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#include <boost/core/exchange.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+void test1()
+{
+    int i = 1;
+    BOOST_TEST(boost::exchange(i, 2) == 1);
+    BOOST_TEST(i == 2);
+}
+
+class C1 {
+public:
+    explicit C1(int i)
+        : i_(i) { }
+    int i() const {
+        return i_;
+    }
+private:
+    int i_;
+};
+
+void test2()
+{
+    C1 x(1);
+    BOOST_TEST(boost::exchange(x, C1(2)).i() == 1);
+    BOOST_TEST(x.i() == 2);
+}
+
+class C2 {
+public:
+    explicit C2(int i)
+        : i_(i) { }
+    operator C1() const {
+        return C1(i_);
+    }
+    int i() const {
+        return i_;
+    }
+private:
+    C2(const C2&);
+    C2& operator=(const C2&);
+    int i_;
+};
+
+void test3()
+{
+    C1 x(1);
+    BOOST_TEST(boost::exchange(x, C2(2)).i() == 1);
+    BOOST_TEST(x.i() == 2);
+}
+
+int main()
+{
+    test1();
+    test2();
+    test3();
+    return boost::report_errors();
+}