Imported existing code
This commit is contained in:
Hazim Gazov
189
libraries/include/boost/proto/transform/when.hpp
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189
libraries/include/boost/proto/transform/when.hpp
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#ifndef BOOST_PP_IS_ITERATING
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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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#ifndef BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
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#define BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
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#include <boost/proto/detail/prefix.hpp>
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#include <boost/preprocessor/cat.hpp>
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#include <boost/preprocessor/repetition/enum_params.hpp>
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#include <boost/preprocessor/repetition/enum_trailing_params.hpp>
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#include <boost/preprocessor/iteration/iterate.hpp>
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#include <boost/mpl/if.hpp>
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#include <boost/proto/proto_fwd.hpp>
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#include <boost/proto/traits.hpp>
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#include <boost/proto/transform/call.hpp>
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#include <boost/proto/transform/make.hpp>
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#include <boost/proto/transform/impl.hpp>
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#include <boost/proto/detail/suffix.hpp>
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namespace boost { namespace proto
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{
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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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/// In <tt>when\<G, T\></tt>, when \c T is a class type it is a
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/// PrimitiveTransform and the following equivalencies hold:
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///
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/// <tt>when\<G,T\>::::result\<void(E,S,V)\>::::type</tt> is the same as
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/// <tt>T::result\<void(E,S,V)\>::::type</tt>.
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///
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/// <tt>when\<G,T\>()(e,s,v)</tt> is the same as
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/// <tt>T()(e,s,v)</tt>.
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template<typename Grammar, typename PrimitiveTransform BOOST_PROTO_WHEN_BUILDING_DOCS(= Grammar)>
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struct when
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: PrimitiveTransform
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{
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typedef typename Grammar::proto_base_expr proto_base_expr;
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};
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/// \brief A specialization that treats function pointer Transforms as
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/// if they were function type Transforms.
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///
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/// This specialization requires that \c Fun is actually a function type.
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///
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/// This specialization is required for nested transforms such as
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/// <tt>when\<G, T0(T1(_))\></tt>. In C++, functions that are used as
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/// parameters to other functions automatically decay to funtion
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/// pointer types. In other words, the type <tt>T0(T1(_))</tt> is
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/// indistinguishable from <tt>T0(T1(*)(_))</tt>. This specialization
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/// is required to handle these nested function pointer type transforms
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/// properly.
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template<typename Grammar, typename Fun>
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struct when<Grammar, Fun *>
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: when<Grammar, Fun>
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{};
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/// \brief Syntactic sugar for <tt>when\<_, Fun\></tt>, for use
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/// in grammars to handle all the cases not yet handled.
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///
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/// Use <tt>otherwise\<T\></tt> in your grammars as a synonym for
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/// <tt>when\<_, T\></tt> 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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template<typename Fun>
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struct otherwise
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: when<_, Fun>
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{};
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#define BOOST_PP_ITERATION_PARAMS_1 (3, (0, BOOST_PROTO_MAX_ARITY, <boost/proto/transform/when.hpp>))
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#include BOOST_PP_ITERATE()
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}} // namespace boost::proto
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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 typename Grammar::proto_base_expr proto_base_expr;
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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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typedef call<R(BOOST_PP_ENUM_PARAMS(N, A))> call_;
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typedef make<R(BOOST_PP_ENUM_PARAMS(N, A))> make_;
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typedef
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typename mpl::if_c<
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// OK to evaluate is_callable<R> here.
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// R should be compete by now.
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is_callable<R>::value
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, call_ // "R" is a function to call
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, make_ // "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>result\<void(Expr, State, Data)\>::::impl()(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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