/Src/Dependencies/Boost/libs/phoenix/doc/inside/placeholder.qbk

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  1. [/==============================================================================
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  2.     Copyright (C) 2001-2010 Joel de Guzman
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  3.     Copyright (C) 2001-2005 Dan Marsden
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  4.     Copyright (C) 2001-2010 Thomas Heller
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  5. 

  6.     Distributed under the Boost Software License, Version 1.0. (See accompanying
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  7.     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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  8. ===============================================================================/]
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  9. 

  10. 

  11. [section Placeholder Unification]
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  12. 

  13. Phoenix uses `boost::is_placeholder` for recognizing placeholders:
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  14. 

  15.     template <typename T>
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  16.     struct is_placeholder
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  17.     {
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  18.         static const int value = 0;
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  19.     };
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  20. 

  21. To adapt your own placeholder, the nested value needs to be greater than 0
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  22. for your types. This is done by specializing this trait.
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  23. 

  24. [endsect]
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