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boost::proto::is_callable — Boolean metafunction which tells whether a type is a callable PolymorphicFunctionObject or not.
// In header: <boost/proto/traits.hpp>
template<typename T>
struct is_callable : mpl::bool_<true-or-false> {
};
proto::is_callable<> is used by the
proto::when<>
transform to determine whether a function type R(A1,...An)
is a CallableTransform or an ObjectTransform.
The former are evaluated using proto::call<>
and the later with proto::make<>.
If proto::is_callable<R>::value is true,
the function type is a CallableTransform; otherwise, it is an ObjectTransform.
Unless specialized for a type
T, proto::is_callable<T>::value
is computed as follows:
If T is a template type
X<Y0,...Yn>,
where all Yx are types for
x in [0,n],
proto::is_callable<T>::value is
boost::is_same<Yn, proto::callable>::value.
If T is derived from proto::callable,
proto::is_callable<T>::value is true.
Otherwise, proto::is_callable<T>::value
is false.