Boost C++ Libraries

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Function unpack_expr

boost::proto::unpack_expr — Construct an expression of the requested tag type with a domain and with children from the specified Fusion Forward Sequence.

Synopsis

// In header: <boost/proto/make_expr.hpp>


template<typename Tag, typename Sequence> 
  typename proto::result_of::unpack_expr<Tag, Sequence const>::type const 
  unpack_expr(Sequence const & sequence);
template<typename Tag, typename Domain, typename Sequence> 
  typename proto::result_of::unpack_expr<Tag, Domain, Sequence const>::type const 
  unpack_expr(Sequence const & sequence);

Description

This function template may be invoked either with or without specifying a Domain argument. If no domain is specified, the domain is deduced by examining in order the domains of the elements of sequence and taking the first that is not proto::default_domain, if any such domain exists, or proto::default_domain otherwise.

Let s be a Fusion Random Access Sequence equivalent to sequence. Let WRAP<N>(s), where s has type S, be defined such that:

  • If fusion::result_of::value_at_c<S,N>::type is a reference, WRAP<N>(s) is equivalent to proto::as_child<Domain>(fusion::at_c<N>(s)).

  • Otherwise, WRAP<N>(s) is equivalent to proto::as_expr<Domain>(fusion::at_c<N>(s)).

Let MAKE<Tag>(a...) be defined as proto::expr<Tag, proto::listN<A...> >::make(a...) where Ax is the type of ax.

Parameters:

sequence

A Fusion Forward Sequence.

Returns:

Domain()(MAKE<Tag>(WRAP<0>(s),... WRAP<N-1>(s))), where N is the size of Sequence.


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