From 16fdb15395bade4d3aaa0768aec5ffcf7ab3ce48 Mon Sep 17 00:00:00 2001
From: Kyle Lutz <kyle.r.lutz@gmail.com>
Date: Fri, 28 Nov 2014 14:08:59 -0800
Subject: [PATCH] Add identity<T>() function

---
 include/boost/compute/detail/meta_kernel.hpp  |  7 ++
 include/boost/compute/functional.hpp          |  1 +
 include/boost/compute/functional/identity.hpp | 64 +++++++++++++++++++
 test/CMakeLists.txt                           |  1 +
 test/test_functional_identity.cpp             | 39 +++++++++++
 5 files changed, 112 insertions(+)
 create mode 100644 include/boost/compute/functional/identity.hpp
 create mode 100644 test/test_functional_identity.cpp

diff --git a/include/boost/compute/detail/meta_kernel.hpp b/include/boost/compute/detail/meta_kernel.hpp
index 544051c7..018f1000 100644
--- a/include/boost/compute/detail/meta_kernel.hpp
+++ b/include/boost/compute/detail/meta_kernel.hpp
@@ -1027,6 +1027,13 @@ inline meta_kernel& operator<<(meta_kernel &k,
     return k << "convert_" << type_name<T>() << "(" << expr.m_arg << ")";
 }
 
+template<class T, class Arg>
+inline meta_kernel& operator<<(meta_kernel &k,
+                               const invoked_identity<T, Arg> &expr)
+{
+    return k << expr.m_arg;
+}
+
 template<>
 struct inject_type_impl<double_>
 {
diff --git a/include/boost/compute/functional.hpp b/include/boost/compute/functional.hpp
index 3b681f52..ea2606ae 100644
--- a/include/boost/compute/functional.hpp
+++ b/include/boost/compute/functional.hpp
@@ -23,6 +23,7 @@
 #include <boost/compute/functional/geometry.hpp>
 #include <boost/compute/functional/get.hpp>
 #include <boost/compute/functional/hash.hpp>
+#include <boost/compute/functional/identity.hpp>
 #include <boost/compute/functional/integer.hpp>
 #include <boost/compute/functional/logical.hpp>
 #include <boost/compute/functional/math.hpp>
diff --git a/include/boost/compute/functional/identity.hpp b/include/boost/compute/functional/identity.hpp
new file mode 100644
index 00000000..95e6da80
--- /dev/null
+++ b/include/boost/compute/functional/identity.hpp
@@ -0,0 +1,64 @@
+//---------------------------------------------------------------------------//
+// Copyright (c) 2013-2014 Kyle Lutz <kyle.r.lutz@gmail.com>
+//
+// 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
+//
+// See http://kylelutz.github.com/compute for more information.
+//---------------------------------------------------------------------------//
+
+#ifndef BOOST_COMPUTE_FUNCTIONAL_IDENTITY_HPP
+#define BOOST_COMPUTE_FUNCTIONAL_IDENTITY_HPP
+
+namespace boost {
+namespace compute {
+namespace detail {
+
+template<class T, class Arg>
+struct invoked_identity
+{
+    typedef T result_type;
+
+    invoked_identity(const Arg &arg)
+        : m_arg(arg)
+    {
+    }
+
+    Arg m_arg;
+};
+
+} // end detail namespace
+
+/// Identity function which simply returns its input.
+///
+/// For example, to directly copy values using the transform() algorithm:
+/// \code
+/// transform(input.begin(), input.end(), output.begin(), identity<int>(), queue);
+/// \endcode
+///
+/// \see as<T>(), convert<T>()
+template<class T>
+class identity
+{
+public:
+    /// Identity function result type.
+    typedef T result_type;
+
+    /// Creates a new identity function.
+    identity()
+    {
+    }
+
+    /// \internal_
+    template<class Arg>
+    detail::invoked_identity<T, Arg> operator()(const Arg &arg) const
+    {
+        return detail::invoked_identity<T, Arg>(arg);
+    }
+};
+
+} // end compute namespace
+} // end boost namespace
+
+#endif // BOOST_COMPUTE_FUNCTIONAL_IDENTITY_HPP
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 2a391eab..33471cff 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -138,6 +138,7 @@ add_compute_test("functional.bind" test_functional_bind.cpp)
 add_compute_test("functional.convert" test_functional_convert.cpp)
 add_compute_test("functional.get" test_functional_get.cpp)
 add_compute_test("functional.hash" test_functional_hash.cpp)
+add_compute_test("functional.identity" test_functional_identity.cpp)
 add_compute_test("functional.popcount" test_functional_popcount.cpp)
 add_compute_test("functional.unpack" test_functional_unpack.cpp)
 
diff --git a/test/test_functional_identity.cpp b/test/test_functional_identity.cpp
new file mode 100644
index 00000000..84cbde53
--- /dev/null
+++ b/test/test_functional_identity.cpp
@@ -0,0 +1,39 @@
+//---------------------------------------------------------------------------//
+// Copyright (c) 2013-2014 Kyle Lutz <kyle.r.lutz@gmail.com>
+//
+// 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
+//
+// See http://kylelutz.github.com/compute for more information.
+//---------------------------------------------------------------------------//
+
+#define BOOST_TEST_MODULE TestFunctionalIdentity
+#include <boost/test/unit_test.hpp>
+
+#include <boost/compute/system.hpp>
+#include <boost/compute/algorithm/transform.hpp>
+#include <boost/compute/container/vector.hpp>
+#include <boost/compute/functional/identity.hpp>
+
+#include "check_macros.hpp"
+#include "context_setup.hpp"
+
+namespace compute = boost::compute;
+
+BOOST_AUTO_TEST_CASE(copy_with_identity_transform)
+{
+    int data[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
+    compute::vector<int> input(data, data + 8, queue);
+    compute::vector<int> output(8, context);
+
+    compute::transform(
+        input.begin(), input.end(), output.begin(), compute::identity<int>(), queue
+    );
+
+    CHECK_RANGE_EQUAL(
+        int, 8, output, (1, 2, 3, 4, 5, 6, 7, 8)
+    );
+}
+
+BOOST_AUTO_TEST_SUITE_END()