Hartmut Kaiser wrote:
Hi all,
is there a means of using the binary visitation pattern provided by the Boost.Variant library and make the return type of the visitation process dependent on the types currently stored inside the visited variant object instances?
When I look at the current apply_visitor interface, I can't think of any: template<typename Visitor, typename Variant> typename Visitor::result_type apply_visitor(Visitor & visitor, Variant & operand); You would need something like the lazy function return type deduction in Phoenix: struct Visitor { template <typename Arg1, typename Arg2> struct result { typedef ... result_type; }; ... }; and template<typename Visitor, typename Variant> typename Visitor::result<???>::result_type apply_visitor(Visitor & visitor, Variant & operand); I really don't know if ??? (the real argument types) can be determined at compile time.
variant_type term1 = 1L; variant_type term2 = 2UL; variant_type term3 = -2L;
variant_type unsigned_result = boost::apply_visitor(add_visitor(), term1, term2); variant_type signed_result = boost::apply_visitor(add_visitor(), term1, term3);
Is this possible with the current implementation?
That's something different: here you assign again to a variant! Why don't you simply use boost::variant as return type for the visitor? Stefan