diff --git a/identity.html b/identity.html
new file mode 100644
index 0000000..ee5b208
--- /dev/null
+++ b/identity.html
@@ -0,0 +1,45 @@
+
+
+
+
+Boost Function Object Adapter Library
+
+
+Identity
+The header
+<boost/functional/identity.hpp> provides the function object
+boost::identity whose operator() returns its
+argument. It is an implementation of C++20's std::identity
+that supports C++03 and above.
+Example
+It is commonly used as the default projection in constrained algorithms.
+
+template<class Range, class Projection = boost::identity>
+void print(Range&& range, Projection projection = {});
+
+Reference
+
+namespace boost {
+
+struct identity {
+ using is_transparent = unspecified;
+
+ template<class T>
+ T&& operator()(T&& value) const noexcept;
+};
+
+} // boost
+
+Operators
+
+template<class T>
+T&& operator()(T&& value) const noexcept;- Returns
std::forward<T>(value)
+
+
+Copyright 2021 Glen Joseph Fernandes.
+Distributed under the
+Boost Software License,
+Version 1.0.
+
+
diff --git a/include/boost/functional/identity.hpp b/include/boost/functional/identity.hpp
new file mode 100644
index 0000000..a4929a9
--- /dev/null
+++ b/include/boost/functional/identity.hpp
@@ -0,0 +1,41 @@
+/*
+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)
+*/
+#ifndef BOOST_FUNCTIONAL_IDENTITY_HPP
+#define BOOST_FUNCTIONAL_IDENTITY_HPP
+
+#include
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#include
+#endif
+
+namespace boost {
+
+struct identity {
+ typedef void is_transparent;
+
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+ template
+ BOOST_CONSTEXPR T&& operator()(T&& value) const BOOST_NOEXCEPT {
+ return std::forward(value);
+ }
+#else
+ template
+ BOOST_CONSTEXPR const T& operator()(const T& value) const BOOST_NOEXCEPT {
+ return value;
+ }
+
+ template
+ BOOST_CONSTEXPR T& operator()(T& value) const BOOST_NOEXCEPT {
+ return value;
+ }
+#endif
+};
+
+} // boost
+
+#endif
diff --git a/index.html b/index.html
index f4315a0..6511667 100644
--- a/index.html
+++ b/index.html
@@ -121,6 +121,12 @@
Based on section 20.3.8 of the standard. |
+
+
+ | Identity |
+ identity |
+ [func.identity] in ISO/IEC 14882:2020 |
+
Usage
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index dbe379c..71de379 100644
--- a/test/Jamfile.v2
+++ b/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 ]
;
diff --git a/test/identity_rvalue_test.cpp b/test/identity_rvalue_test.cpp
new file mode 100644
index 0000000..d4af64d
--- /dev/null
+++ b/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
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#include
+#include
+#include
+#include
+#include
+#include
+
+enum kind {
+ rvalue,
+ crvalue,
+ other
+};
+
+kind result(std::string&&)
+{
+ return rvalue;
+}
+
+kind result(const std::string&&)
+{
+ return crvalue;
+}
+
+template
+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 v1;
+ v1.push_back(std::string("a"));
+ v1.push_back(std::string("b"));
+ v1.push_back(std::string("c"));
+ std::vector v2(v1);
+ std::vector 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
diff --git a/test/identity_test.cpp b/test/identity_test.cpp
new file mode 100644
index 0000000..81dc239
--- /dev/null
+++ b/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
+#include
+#include
+#include
+#include
+#include
+
+enum kind {
+ ref,
+ cref,
+ other
+};
+
+kind result(std::string&)
+{
+ return ref;
+}
+
+kind result(const std::string&)
+{
+ return cref;
+}
+
+template
+kind result(T&)
+{
+ return other;
+}
+
+template
+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 v1;
+ v1.push_back(std::string("a"));
+ v1.push_back(std::string("b"));
+ v1.push_back(std::string("c"));
+ std::vector 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();
+}