Add identity<T>() function

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_>
 {

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>

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