/////////////////////////////////////////////////////////////////////////////// /// \file lazy.hpp /// Contains definition of the lazy<> transform. // // Copyright 2008 Eric Niebler. Distributed under the Boost // Software License, Version 1.0. (See accompanying file // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) #ifndef BOOST_PROTO_TRANSFORM_LAZY_HPP_EAN_12_02_2007 #define BOOST_PROTO_TRANSFORM_LAZY_HPP_EAN_12_02_2007 #include <boost/preprocessor/iteration/iterate.hpp> #include <boost/preprocessor/repetition/enum_params.hpp> #include <boost/preprocessor/repetition/enum_trailing_params.hpp> #include <boost/proto/proto_fwd.hpp> #include <boost/proto/transform/make.hpp> #include <boost/proto/transform/call.hpp> #include <boost/proto/transform/impl.hpp> #include <boost/proto/transform/detail/pack.hpp> namespace boost { namespace proto { /// \brief A PrimitiveTransform that uses <tt>make\<\></tt> to build /// a CallableTransform, and then uses <tt>call\<\></tt> to apply it. /// /// <tt>lazy\<\></tt> is useful as a higher-order transform, when the /// transform to be applied depends on the current state of the /// transformation. The invocation of the <tt>make\<\></tt> transform /// evaluates any nested transforms, and the resulting type is treated /// as a CallableTransform, which is evaluated with <tt>call\<\></tt>. template<typename Object> struct lazy : transform<lazy<Object> > { template<typename Expr, typename State, typename Data> struct impl : call< typename make<Object>::template impl<Expr, State, Data>::result_type >::template impl<Expr, State, Data> {}; }; /// INTERNAL ONLY template<typename Fun> struct lazy<detail::msvc_fun_workaround<Fun> > : lazy<Fun> {}; #include <boost/proto/transform/detail/lazy.hpp> /// INTERNAL ONLY /// template<typename Object> struct is_callable<lazy<Object> > : mpl::true_ {}; }} #endif