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Struct template _child_c

boost::proto::_child_c — A PrimitiveTransform that returns N-th child of the current expression.


// In header: <boost/proto/transform/arg.hpp>

template<int N> 
struct _child_c :  proto::transform< _child_c<N> > {
  template<typename Expr, typename State, typename Data> 
  struct impl :  proto::transform_impl< Expr, State, Data > {
    // types
    typedef typename proto::result_of::child_c< Expr, N >::type result_type;

    // public member functions
    typename proto::result_of::child_c< Expr, N >::type 
    operator()(typename impl::expr_param, typename impl::state_param, 
               typename impl::data_param) const;



proto::terminal<int>::type i = {42};
proto::terminal<int>::type & j = proto::_child_c<0>()(-i);
assert( boost::addressof(i) == boost::addressof(j) );