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109 lines
4.2 KiB
109 lines
4.2 KiB
#if !defined(BOOST_PROTO_DONT_USE_PREPROCESSED_FILES) |
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#include <boost/proto/transform/detail/preprocessed/when.hpp> |
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#elif !defined(BOOST_PP_IS_ITERATING) |
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#if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES) |
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#pragma wave option(preserve: 2, line: 0, output: "preprocessed/when.hpp") |
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#endif |
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/////////////////////////////////////////////////////////////////////////////// |
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/// \file when.hpp |
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/// Definition of when transform. |
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// |
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// Copyright 2008 Eric Niebler. Distributed under the Boost |
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// Software License, Version 1.0. (See accompanying file |
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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#if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES) |
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#pragma wave option(preserve: 1) |
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#endif |
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#define BOOST_PP_ITERATION_PARAMS_1 \ |
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(3, (0, BOOST_PROTO_MAX_ARITY, <boost/proto/transform/detail/when.hpp>)) |
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#include BOOST_PP_ITERATE() |
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#if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES) |
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#pragma wave option(output: null) |
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#endif |
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#else |
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#define N BOOST_PP_ITERATION() |
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/// \brief A grammar element and a PrimitiveTransform that associates |
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/// a transform with the grammar. |
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/// |
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/// Use <tt>when\<\></tt> to override a grammar's default transform |
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/// with a custom transform. It is for used when composing larger |
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/// transforms by associating smaller transforms with individual |
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/// rules in your grammar, as in the following transform which |
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/// counts the number of terminals in an expression. |
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/// |
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/// \code |
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/// // Count the terminals in an expression tree. |
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/// // Must be invoked with initial state == mpl::int_<0>(). |
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/// struct CountLeaves |
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/// : or_< |
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/// when<terminal<_>, mpl::next<_state>()> |
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/// , otherwise<fold<_, _state, CountLeaves> > |
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/// > |
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/// {}; |
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/// \endcode |
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/// |
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/// The <tt>when\<G, R(A0,A1,...)\></tt> form accepts either a |
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/// CallableTransform or an ObjectTransform as its second parameter. |
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/// <tt>when\<\></tt> uses <tt>is_callable\<R\>::value</tt> to |
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/// distinguish between the two, and uses <tt>call\<\></tt> to |
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/// evaluate CallableTransforms and <tt>make\<\></tt> to evaluate |
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/// ObjectTransforms. |
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template<typename Grammar, typename R BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)> |
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struct when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A))> |
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: transform<when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A))> > |
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{ |
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typedef Grammar first; |
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typedef R second(BOOST_PP_ENUM_PARAMS(N, A)); |
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typedef typename Grammar::proto_grammar proto_grammar; |
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// Note: do not evaluate is_callable<R> in this scope. |
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// R may be an incomplete type at this point. |
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template<typename Expr, typename State, typename Data> |
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struct impl : transform_impl<Expr, State, Data> |
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{ |
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// OK to evaluate is_callable<R> here. R should be compete by now. |
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typedef |
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typename mpl::if_c< |
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is_callable<R>::value |
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, call<R(BOOST_PP_ENUM_PARAMS(N, A))> // "R" is a function to call |
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, make<R(BOOST_PP_ENUM_PARAMS(N, A))> // "R" is an object to construct |
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>::type |
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which; |
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typedef typename which::template impl<Expr, State, Data>::result_type result_type; |
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/// Evaluate <tt>R(A0,A1,...)</tt> as a transform either with |
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/// <tt>call\<\></tt> or with <tt>make\<\></tt> depending on |
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/// whether <tt>is_callable\<R\>::value</tt> is \c true or |
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/// \c false. |
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/// |
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/// \param e The current expression |
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/// \param s The current state |
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/// \param d An arbitrary data |
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/// \pre <tt>matches\<Expr, Grammar\>::value</tt> is \c true |
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/// \return <tt>which()(e, s, d)</tt> |
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result_type operator ()( |
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typename impl::expr_param e |
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, typename impl::state_param s |
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, typename impl::data_param d |
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) const |
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{ |
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return typename which::template impl<Expr, State, Data>()(e, s, d); |
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} |
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}; |
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}; |
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#undef N |
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#endif
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