Struct template switch_ . Boost , The Boost C++ Libraries BoostBook Documentation Subset , Reference

Struct template switch_

boost::proto::switch_ — For matching one of a set of alternate grammars, which are looked up based on the result type of the transform passed in second template parameter. If no transform is passed, the default one is proto::tag_of<proto::_>() so the default matching is based on the expression's tag type. When used as a transform, proto::switch_<> applies the transform associated with the sub-grammar that matches the expression.

Synopsis

// In header: <boost/proto/matches.hpp>
template<typename Cases, typename Transform> 
struct switch_ :  proto::transform<switch_<Cases, Transform> > {
  // types
  typedef switch_ proto_grammar;
  // member classes/structs/unions
  template<typename Expr, typename State, typename Data> 
  struct impl :  
    Cases::template case_<
      typename when<_, Transform>::template impl<Expr, State, Data>::result_type 
    >::template impl<Expr, State, Data>
  {
  };
};

Description

Тип выражения<E>матчи<proto::switch_<C,T>>, если<E>матчи<C::case_<boost::result_of<proto::when<proto::_,T>(E)>::type>>.

При применении<proto::switch_<C,T>>в качестве преобразования с выражением<e>типа<E>, состояния<s>типа<S>и данных<d>типа<D>он эквивалентен<C::case_<boost::result_of<proto::when<proto::_,T>(E,S,D)>::type>()(e, s, d)>.

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