Adapts a visitor for use as a function object. Adapts the function given at construction for use as a function object. This is useful, for example, when one needs to operate on each element of a sequence of variant objects using a standard library algorithm such as std::for_each. See the "visitor-only" form of apply_visitor for a simple way to create apply_visitor_delayed_t objects. typename Visitor::result_type Visitor & Constructs the function object with the given visitor. result_type Variant & result_type Variant1 & Variant2 & Function call operator. Invokes apply_visitor on the stored visitor using the given operands. typename Visitor::result_type Visitor & Variant & typename Visitor::result_type const Visitor & Variant & typename BinaryVisitor::result_type BinaryVisitor & Variant1 & Variant2 & typename BinaryVisitor::result_type const BinaryVisitor & Variant1 & Variant2 & typename MultiVisitor::result_type MultiVisitor & Variant1 & Variant2 & Variant3 & ... typename MultiVisitor::result_type const MultiVisitor & Variant1 & Variant2 & Variant3 & ... apply_visitor_delayed_t<Visitor> 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. The behavior of apply_visitor is dependent on the number of arguments on which it operates (i.e., other than the visitor). The function behaves as follows: Overloads accepting one operand invoke the unary function call operator of the given visitor on the content of the given variant operand. Overloads accepting two operands invoke the binary function call operator of the given visitor on the content of the given variant operands. Overloads accepting three or more operands invoke the function call operator of the given visitor on the content of the given variant operands. Maximum amount of parameters controlled by BOOST_VARAINT_MAX_MULTIVIZITOR_PARAMS macro. Those functions are actually defined in . The overload accepting only a visitor returns a generic function object that accepts either one or two arguments and invokes apply_visitor using these arguments and visitor, thus behaving as specified above. (This behavior is particularly useful, for example, when one needs to operate on each element of a sequence of variant objects using a standard library algorithm.) The overloads acccepting operands return the result of applying the given visitor to the content of the given operands. The overload accepting only a visitor return a function object, thus delaying application of the visitor to any operands. The given visitor must fulfill the StaticVisitor concept requirements with respect to each of the bounded types of the given variant. The overloads accepting operands throw only if the given visitor throws when applied. The overload accepting only a visitor will not throw. (Note, however, that the returned function object may throw when invoked.)