1 2 // Copyright (C) 2009-2012 Lorenzo Caminiti 3 // Distributed under the Boost Software License, Version 1.0 4 // (see accompanying file LICENSE_1_0.txt or a copy at 5 // http://www.boost.org/LICENSE_1_0.txt) 6 // Home at http://www.boost.org/libs/utility/identity_type 7 8 /** @file 9 Wrap type expressions with round parenthesis so they can be passed to macros 10 even if they contain commas. 11 */ 12 13 #ifndef BOOST_IDENTITY_TYPE_HPP_ 14 #define BOOST_IDENTITY_TYPE_HPP_ 15 16 #include <boost/type_traits/function_traits.hpp> 17 18 /** 19 @brief This macro allows to wrap the specified type expression within extra 20 round parenthesis so the type can be passed as a single macro parameter even if 21 it contains commas (not already wrapped within round parenthesis). 22 23 @Params 24 @Param{parenthesized_type, 25 The type expression to be passed as macro parameter wrapped by a single set 26 of round parenthesis <c>(...)</c>. 27 This type expression can contain an arbitrary number of commas. 28 } 29 @EndParams 30 31 This macro works on any C++03 compiler (it does not use variadic macros). 32 33 This macro must be prefixed by <c>typename</c> when used within templates. 34 Note that the compiler will not be able to automatically determine function 35 template parameters when they are wrapped with this macro (these parameters 36 need to be explicitly specified when calling the function template). 37 38 On some compilers (like GCC), using this macro on abstract types requires to 39 add and remove a reference to the specified type. 40 */ 41 #define BOOST_IDENTITY_TYPE(parenthesized_type) \ 42 /* must NOT prefix this with `::` to work with parenthesized syntax */ \ 43 boost::function_traits< void parenthesized_type >::arg1_type 44 45 #endif // #include guard 46 47