1[/============================================================================== 2 Copyright (C) 2001-2010 Joel de Guzman 3 Copyright (C) 2001-2005 Dan Marsden 4 Copyright (C) 2001-2010 Thomas Heller 5 6 Distributed under the Boost Software License, Version 1.0. (See accompanying 7 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 8===============================================================================/] 9 10 11[section Placeholder Unification] 12 13Phoenix uses `boost::is_placeholder` for recognizing placeholders: 14 15 template <typename T> 16 struct is_placeholder 17 { 18 static const int value = 0; 19 }; 20 21To adapt your own placeholder, the nested value needs to be greater than 0 22for your types. This is done by specializing this trait. 23 24[endsect] 25