...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::proto::is_expr — A Boolean metafunction that indicates whether a given type T
is a Proto expression type.
// In header: <boost/proto/traits.hpp>
template<typename T>
struct is_expr : mpl::bool_<true-or-false
> {
};
If T
is an instantiation of
proto::expr<>
or
proto::basic_expr<>
or is an extension
(via proto::extends<> or
BOOST_PROTO_EXTENDS()) of such an instantiation,
proto::is_expr<T>::value
is true
.
Otherwise, proto::is_expr<T>::value
is false
.