Provides declarations of apply_visitor for three or more variant parameters. Controls maximum amount of variant parameters for multi visistors. Not used when std::tuple is available and BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES is not defined. Note: Default amount is 4. Define it to bigger value before including <boost/variant/multivisitors.hpp> to increase maximum amount of variant parameters for apply_visitor. Allows compile-time checked type-safe application of the given visitor to the content of the given variant, ensuring that all types are handled by the visitor. See apply_visitor for more information. typename MultiVisitor::result_type OR decltype(auto) MultiVisitor & Variant1&& Variant2&& Variant3&& ... typename MultiVisitor::result_type OR decltype(auto) const MultiVisitor & Variant1&& Variant2&& Variant3&& ...