boost::proto::_ Struct Reference

A wildcard grammar element that matches any expression, and a transform that returns the current expression unchanged. More...

#include <matches.hpp>

Inheritance diagram for boost::proto::_:

Collaboration diagram for boost::proto::_:

Classes
struct	impl

Public Types
typedef _	proto_grammar
typedef _	transform_type

Public Member Functions
	BOOST_PROTO_CALLABLE () typedef X proto_is_transform_
BOOST_FORCEINLINE boost::proto::detail::apply_transform < transform_type(Expr const &)> ::result_type	operator() (Expr &&e) const
BOOST_FORCEINLINE boost::proto::detail::apply_transform < transform_type(Expr const &, State const &)> ::result_type	operator() (Expr &&e, State &&s) const
BOOST_FORCEINLINE boost::proto::detail::apply_transform < transform_type(Expr const &, State const &, Data const &)> ::result_type	operator() (Expr &&e, State &&s, Data &&d) const

Detailed Description

A wildcard grammar element that matches any expression, and a transform that returns the current expression unchanged.

The wildcard type, _, is a grammar element such that matches<E,_>value is true for any expression type E.

The wildcard can also be used as a stand-in for a template argument when matching terminals. For instance, the following is a grammar that will match any std::complex<> terminal:

BOOST_MPL_ASSERT((
    matches<
        terminal<std::complex<double> >::type
      , terminal<std::complex< _ > >
    >
));

When used as a transform, _ returns the current expression unchanged. For instance, in the following, _ is used with the fold<> transform to fold the children of a node:

struct CountChildren
  : or_<
        // Terminals have no children
        when<terminal<_>, mpl::int_<0>()>
        // Use fold<> to count the children of non-terminals
      , otherwise<
            fold<
                _ // <-- fold the current expression
              , mpl::int_<0>()
              , mpl::plus<_state, mpl::int_<1> >()
            >
        >
    >
{};

Member Typedef Documentation

typedef _ boost::proto::_::proto_grammar

typedef _ boost::proto::transform< _ , X >::transform_type

inherited

Member Function Documentation

boost::proto::transform< _ , X >::BOOST_PROTO_CALLABLE ( )

inherited

BOOST_FORCEINLINE boost::proto::detail::apply_transform<transform_type(Expr const &, State const &, Data const &)>::result_type boost::proto::transform< _ , X >::operator() ( Expr &&  e, State &&  s, Data &&  d  ) const

inlineinherited

BOOST_FORCEINLINE boost::proto::detail::apply_transform<transform_type(Expr const &, State const &)>::result_type boost::proto::transform< _ , X >::operator() ( Expr &&  e, State &&  s  ) const

inlineinherited

BOOST_FORCEINLINE boost::proto::detail::apply_transform<transform_type(Expr const &)>::result_type boost::proto::transform< _ , X >::operator() ( Expr &&  e ) const

inlineinherited

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The documentation for this struct was generated from the following file:

• boost_1_57_0/boost/proto/matches.hpp