Adam Badura wrote:
Obviously it would not be wise to provide a function wrapper for each and every visitor. However the extended "get" I proposed is unique in its ways.
But it wouldn't be 'get'. There is a reason why it works like this. It's designed to test and extract for a specific type in one of the variant possibilities, without doing any implicit conversion. Adding the enhancement you suggest would change the meaning of 'get' and potentially break other code. So I think it would be best as a separate function. Here is a possible implementation: namespace boost { namespace detail { template<typename T> struct extract_visitor : static_visitor<T&> { T& operator()(T& t) const { return t; } T operator()(...) const { throw bad_visit(); } }; template<typename T> struct extract_pointer_visitor : static_visitor<T*> { T* operator()(T& t) const { return &t; } T* operator()(...) const { return 0; } }; } // namespace detail template<typename T, typename Variant> T& extract(Variant& v) { return apply_visitor(detail::extract_visitor<T>(), v); } template<typename T, typename Variant> const T& extract(const Variant& v) { return apply_visitor(detail::extract_visitor<const T>(), v); } template<typename T, typename Variant> T* extract(Variant* v) { return apply_visitor(detail::extract_pointer_visitor<T>(), *v); } template<typename T, typename Variant> const T* extract(const Variant* v) { return apply_visitor(detail::extract_pointer_visitor<const T>(), *v); } } // namespace boost
Secondly it provides for variant a feature available in union.
That could only work with unions if the types are binary compatible, which isn't necessarily the case.