Add identity function object

test/Jamfile.v2

@@ -6,4 +6,6 @@ import testing ;
 
 test-suite functional :
     [ run function_test.cpp ]
+    [ run identity_test.cpp ]
+    [ run identity_rvalue_test.cpp ]
     ;

test/identity_rvalue_test.cpp

@@ -0,0 +1,75 @@
+/*
+Copyright 2021 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/functional/identity.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <algorithm>
+#include <iterator>
+#include <string>
+#include <vector>
+
+enum kind {
+    rvalue,
+    crvalue,
+    other
+};
+
+kind result(std::string&&)
+{
+    return rvalue;
+}
+
+kind result(const std::string&&)
+{
+    return crvalue;
+}
+
+template<class T>
+kind result(T&&)
+{
+    return other;
+}
+
+void simple_test()
+{
+    typedef std::string string;
+    BOOST_TEST(boost::identity()(string("a")) == string("a"));
+    BOOST_TEST(result(boost::identity()(string("a"))) == rvalue);
+    typedef const std::string cstring;
+    BOOST_TEST(boost::identity()(cstring("a")) == cstring("a"));
+    BOOST_TEST(result(boost::identity()(cstring("a"))) == crvalue);
+}
+
+void algorithm_test()
+{
+    std::vector<std::string> v1;
+    v1.push_back(std::string("a"));
+    v1.push_back(std::string("b"));
+    v1.push_back(std::string("c"));
+    std::vector<std::string> v2(v1);
+    std::vector<std::string> v3;
+    std::transform(std::make_move_iterator(v2.begin()),
+        std::make_move_iterator(v2.end()),
+        std::back_inserter(v3),
+        boost::identity());
+    BOOST_TEST(v3 == v1);
+}
+
+int main()
+{
+    simple_test();
+    algorithm_test();
+    return boost::report_errors();
+}
+#else
+int main()
+{
+    return 0;
+}
+#endif

test/identity_test.cpp

@@ -0,0 +1,72 @@
+/*
+Copyright 2021 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/functional/identity.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <algorithm>
+#include <iterator>
+#include <string>
+#include <vector>
+
+enum kind {
+    ref,
+    cref,
+    other
+};
+
+kind result(std::string&)
+{
+    return ref;
+}
+
+kind result(const std::string&)
+{
+    return cref;
+}
+
+template<class T>
+kind result(T&)
+{
+    return other;
+}
+
+template<class T>
+kind result(const T&)
+{
+    return other;
+}
+
+void simple_test()
+{
+    std::string s1("a");
+    BOOST_TEST(boost::identity()(s1) == s1);
+    BOOST_TEST(&boost::identity()(s1) == &s1);
+    BOOST_TEST(result(boost::identity()(s1)) == ref);
+    const std::string s2("a");
+    BOOST_TEST(boost::identity()(s2) == s2);
+    BOOST_TEST(&boost::identity()(s2) == &s2);
+    BOOST_TEST(result(boost::identity()(s2)) == cref);
+}
+
+void algorithm_test()
+{
+    std::vector<std::string> v1;
+    v1.push_back(std::string("a"));
+    v1.push_back(std::string("b"));
+    v1.push_back(std::string("c"));
+    std::vector<std::string> v2;
+    std::transform(v1.begin(), v1.end(), std::back_inserter(v2),
+         boost::identity());
+    BOOST_TEST(v2 == v1);
+}
+
+int main()
+{
+    simple_test();
+    algorithm_test();
+    return boost::report_errors();
+}