Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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Function as_expr

boost::proto::as_expr — A function that wraps non-Proto expression types in Proto terminals and leaves Proto expression types alone.

Synopsis

template<typename T> 
  typename proto::result_of::as_expr< T >::type as_expr(T & t);
template<typename T> 
  typename proto::result_of::as_expr< T const >::type as_expr(T const & t);
template<typename Domain, typename T> 
  typename proto::result_of::as_expr< T, Domain >::type as_expr(T & t);
template<typename Domain, typename T> 
  typename proto::result_of::as_expr< T const, Domain >::type 
  as_expr(T const & t);

Description

The proto::as_expr() function turns objects into Proto terminals if they are not Proto expression types already. Non-Proto types are held by value, if possible. Types which are already Proto types are left alone.

This function can be called either with an explicitly specified Domain parameter (i.e., proto::as_expr<Domain>(t)), or without (i.e., proto::as_expr(t)). If no domain is specified, proto::default_domain is assumed.

If proto::is_expr<T>::value is true, then the argument is returned unmodified. Otherwise, the argument is wrapped in a Proto terminal expression node according to the following rules. If T is a function type, let A be T &. Otherwise, let A be the type T stripped of cv-qualifiers. Then, proto::as_expr() returns Domain()(proto::terminal<A>::type::make(t)).


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