ceph/src/boost/libs/proto/include/boost/proto/transform/lazy.hpp

   1 ///////////////////////////////////////////////////////////////////////////////
   2 /// \file lazy.hpp
   3 /// Contains definition of the lazy<> transform.
   4 //
   5 //  Copyright 2008 Eric Niebler. Distributed under the Boost
   6 //  Software License, Version 1.0. (See accompanying file
   7 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   8
   9 #ifndef BOOST_PROTO_TRANSFORM_LAZY_HPP_EAN_12_02_2007
  10 #define BOOST_PROTO_TRANSFORM_LAZY_HPP_EAN_12_02_2007
  11
  12 #include <boost/preprocessor/iteration/iterate.hpp>
  13 #include <boost/preprocessor/repetition/enum_params.hpp>
  14 #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
  15 #include <boost/proto/proto_fwd.hpp>
  16 #include <boost/proto/transform/make.hpp>
  17 #include <boost/proto/transform/call.hpp>
  18 #include <boost/proto/transform/impl.hpp>
  19 #include <boost/proto/transform/detail/pack.hpp>
  20
  21 namespace boost { namespace proto
  22 {
  23     /// \brief A PrimitiveTransform that uses <tt>make\<\></tt> to build
  24     /// a CallableTransform, and then uses <tt>call\<\></tt> to apply it.
  25     ///
  26     /// <tt>lazy\<\></tt> is useful as a higher-order transform, when the
  27     /// transform to be applied depends on the current state of the
  28     /// transformation. The invocation of the <tt>make\<\></tt> transform
  29     /// evaluates any nested transforms, and the resulting type is treated
  30     /// as a CallableTransform, which is evaluated with <tt>call\<\></tt>.
  31     template<typename Object>
  32     struct lazy : transform<lazy<Object> >
  33     {
  34         template<typename Expr, typename State, typename Data>
  35         struct impl
  36           : call<
  37                 typename make<Object>::template impl<Expr, State, Data>::result_type
  38             >::template impl<Expr, State, Data>
  39         {};
  40     };
  41
  42     /// INTERNAL ONLY
  43     template<typename Fun>
  44     struct lazy<detail::msvc_fun_workaround<Fun> >
  45       : lazy<Fun>
  46     {};
  47
  48     #include <boost/proto/transform/detail/lazy.hpp>
  49
  50     /// INTERNAL ONLY
  51     ///
  52     template<typename Object>
  53     struct is_callable<lazy<Object> >
  54       : mpl::true_
  55     {};
  56
  57 }}
  58
  59 #endif