boost/utility/identity_type.hpp

0001
0002 // Copyright (C) 2009-2012 Lorenzo Caminiti
0003 // Distributed under the Boost Software License, Version 1.0
0004 // (see accompanying file LICENSE_1_0.txt or a copy at
0005 // http://www.boost.org/LICENSE_1_0.txt)
0006 // Home at http://www.boost.org/libs/utility/identity_type
0007
0008 /** @file
0009 Wrap type expressions with round parenthesis so they can be passed to macros
0010 even if they contain commas.
0011 */
0012
0013 #ifndef BOOST_IDENTITY_TYPE_HPP_
0014 #define BOOST_IDENTITY_TYPE_HPP_
0015
0016 #include <boost/type_traits/function_traits.hpp>
0017
0018 /**
0019 @brief This macro allows to wrap the specified type expression within extra
0020 round parenthesis so the type can be passed as a single macro parameter even if
0021 it contains commas (not already wrapped within round parenthesis).
0022
0023 @Params
0024 @Param{parenthesized_type,
0025 The type expression to be passed as macro parameter wrapped by a single set
0026 of round parenthesis <c>(...)</c>.
0027 This type expression can contain an arbitrary number of commas.
0028 }
0029 @EndParams
0030
0031 This macro works on any C++03 compiler (it does not use variadic macros).
0032
0033 This macro must be prefixed by <c>typename</c> when used within templates.
0034 Note that the compiler will not be able to automatically determine function
0035 template parameters when they are wrapped with this macro (these parameters
0036 need to be explicitly specified when calling the function template).
0037
0038 On some compilers (like GCC), using this macro on abstract types requires to
0039 add and remove a reference to the specified type.
0040 */
0041 #define BOOST_IDENTITY_TYPE(parenthesized_type) \
0042     /* must NOT prefix this with `::` to work with parenthesized syntax */ \
0043     boost::function_traits< void parenthesized_type >::arg1_type
0044
0045 #endif // #include guard
0046