360 lines
10 KiB
Plaintext
360 lines
10 KiB
Plaintext
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///////////////////////////////////////////////////////////////////////////////
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/// \file arg.hpp
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/// Contains definition of the argN transforms.
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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_ARG_HPP_EAN_11_01_2007
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#define BOOST_PROTO_TRANSFORM_ARG_HPP_EAN_11_01_2007
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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/impl.hpp>
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#include <boost/type_traits/is_array.hpp>
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#include <boost/proto/transform/env.hpp>
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namespace boost { namespace proto
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{
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/// \brief A PrimitiveTransform that returns the current expression
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/// unmodified
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///
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/// Example:
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///
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/// \code
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/// proto::terminal<int>::type i = {42};
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/// proto::terminal<int>::type & j = proto::_expr()(i);
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/// assert( boost::addressof(i) == boost::addressof(j) );
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/// \endcode
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struct _expr : transform<_expr>
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{
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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 Expr result_type;
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/// Returns the current expression.
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/// \param e The current expression.
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/// \return \c e
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/// \throw nothrow
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BOOST_PROTO_RETURN_TYPE_STRICT_LOOSE(result_type, typename impl::expr_param)
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operator()(
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typename impl::expr_param e
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, typename impl::state_param
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, typename impl::data_param
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) const
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{
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return e;
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}
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};
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};
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/// \brief A PrimitiveTransform that returns the current state
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/// unmodified
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///
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/// Example:
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///
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/// \code
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/// proto::terminal<int>::type i = {42};
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/// char ch = proto::_state()(i, 'a');
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/// assert( ch == 'a' );
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/// \endcode
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struct _state : transform<_state>
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{
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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 State result_type;
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/// Returns the current state.
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/// \param s The current state.
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/// \return \c s
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/// \throw nothrow
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BOOST_PROTO_RETURN_TYPE_STRICT_LOOSE(result_type, typename impl::state_param)
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operator ()(
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typename impl::expr_param
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, typename impl::state_param s
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, typename impl::data_param
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) const
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{
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return s;
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}
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};
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};
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/// \brief A PrimitiveTransform that returns the current data
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/// unmodified
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///
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/// Example:
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///
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/// \code
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/// proto::terminal<int>::type i = {42};
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/// std::string str("hello");
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/// std::string & data = proto::_data()(i, 'a', str);
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/// assert( &str == &data );
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/// \endcode
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struct _data : transform<_data>
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{
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template<typename Expr, typename State, typename Data>
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struct impl
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: mpl::if_c<
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is_env<Data>::value
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, _env_var<data_type>
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, _env
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>::type::template impl<Expr, State, Data>
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{};
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};
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/// \brief A PrimitiveTransform that returns N-th child of the current
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/// expression.
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///
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/// Example:
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///
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/// \code
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/// proto::terminal<int>::type i = {42};
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/// proto::terminal<int>::type & j = proto::_child_c<0>()(-i);
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/// assert( boost::addressof(i) == boost::addressof(j) );
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/// \endcode
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template<int N>
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struct _child_c : transform<_child_c<N> >
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{
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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
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typename result_of::child_c<Expr, N>::type
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result_type;
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/// Returns the N-th child of \c e
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/// \pre <tt>arity_of\<Expr\>::value \> N</tt>
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/// \param e The current expression.
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/// \return <tt>proto::child_c\<N\>(e)</tt>
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/// \throw nothrow
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#ifdef BOOST_PROTO_STRICT_RESULT_OF
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result_type
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#else
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typename result_of::child_c<typename impl::expr_param, N>::type
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#endif
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operator ()(
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typename impl::expr_param e
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, typename impl::state_param
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, typename impl::data_param
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) const
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{
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return proto::child_c<N>(e);
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}
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};
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};
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/// \brief A PrimitiveTransform that returns the value of the
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/// current terminal expression.
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///
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/// Example:
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///
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/// \code
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/// proto::terminal<int>::type i = {42};
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/// int j = proto::_value()(i);
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/// assert( 42 == j );
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/// \endcode
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struct _value : transform<_value>
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{
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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
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typename result_of::value<Expr>::type
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result_type;
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/// Returns the value of the specified terminal expression.
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/// \pre <tt>arity_of\<Expr\>::value == 0</tt>.
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/// \param e The current expression.
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/// \return <tt>proto::value(e)</tt>
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/// \throw nothrow
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#ifdef BOOST_PROTO_STRICT_RESULT_OF
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typename mpl::if_c<is_array<result_type>::value, result_type &, result_type>::type
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#else
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typename result_of::value<typename impl::expr_param>::type
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#endif
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operator ()(
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typename impl::expr_param e
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, typename impl::state_param
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, typename impl::data_param
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) const
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{
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return proto::value(e);
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}
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};
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};
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/// \brief A PrimitiveTransform that does nothing
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/// and returns void.
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struct _void : transform<_void>
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{
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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 void result_type;
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/// Does nothing and returns void
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void operator ()(
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typename impl::expr_param
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, typename impl::state_param
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, typename impl::data_param
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) const
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{}
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};
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};
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/// \brief A unary CallableTransform that wraps its argument
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/// in a \c boost::reference_wrapper\<\>.
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///
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/// Example:
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///
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/// \code
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/// proto::terminal<int>::type i = {42};
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/// boost::reference_wrapper<proto::terminal<int>::type> j
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/// = proto::when<_, proto::_byref(_)>()(i);
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/// assert( boost::addressof(i) == boost::addressof(j.get()) );
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/// \endcode
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struct _byref : callable
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{
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template<typename Sig>
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struct result;
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template<typename This, typename T>
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struct result<This(T)>
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{
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typedef boost::reference_wrapper<T const> const type;
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};
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template<typename This, typename T>
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struct result<This(T &)>
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{
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typedef boost::reference_wrapper<T> const type;
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};
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/// Wrap the parameter \c t in a \c boost::reference_wrapper\<\>
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/// \param t The object to wrap
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/// \return <tt>boost::ref(t)</tt>
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/// \throw nothrow
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template<typename T>
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boost::reference_wrapper<T> const operator ()(T &t) const
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{
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return boost::reference_wrapper<T>(t);
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}
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/// \overload
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///
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template<typename T>
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boost::reference_wrapper<T const> const operator ()(T const &t) const
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{
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return boost::reference_wrapper<T const>(t);
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}
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};
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/// \brief A unary CallableTransform that strips references
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/// and \c boost::reference_wrapper\<\> from its argument.
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///
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/// Example:
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///
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/// \code
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/// proto::terminal<int>::type i = {42};
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/// int j = 67;
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/// int k = proto::when<_, proto::_byval(proto::_state)>()(i, boost::ref(j));
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/// assert( 67 == k );
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/// \endcode
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struct _byval : callable
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{
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template<typename Sig>
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struct result;
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template<typename This, typename T>
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struct result<This(T)>
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{
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typedef T type;
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};
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template<typename This, typename T>
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struct result<This(T &)>
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: result<This(T)>
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{};
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template<typename This, typename T>
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struct result<This(boost::reference_wrapper<T>)>
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: result<This(T)>
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{};
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/// \param t The object to unref
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/// \return <tt>t</tt>
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/// \throw nothrow
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template<typename T>
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T operator ()(T const &t) const
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{
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return t;
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}
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/// \overload
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///
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template<typename T>
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T operator ()(boost::reference_wrapper<T> const &t) const
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{
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return t;
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}
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};
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/// INTERNAL ONLY
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///
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template<>
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struct is_callable<_expr>
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: mpl::true_
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{};
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/// INTERNAL ONLY
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///
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template<>
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struct is_callable<_state>
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: mpl::true_
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{};
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/// INTERNAL ONLY
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///
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template<>
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struct is_callable<_data>
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: mpl::true_
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{};
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/// INTERNAL ONLY
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///
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template<int N>
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struct is_callable<_child_c<N> >
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: mpl::true_
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{};
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/// INTERNAL ONLY
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///
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template<>
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struct is_callable<_value>
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: mpl::true_
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{};
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/// INTERNAL ONLY
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///
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template<>
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struct is_callable<_byref>
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: mpl::true_
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{};
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/// INTERNAL ONLY
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///
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template<>
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struct is_callable<_byval>
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: mpl::true_
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{};
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}}
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#endif
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