Function apply

Function apply_visitor

boost::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.

Synopsis

template<typename Visitor, typename Variant> 
  typename Visitor::result_type 
  apply_visitor(Visitor & visitor, Variant & operand);
template<typename Visitor, typename Variant> 
  typename Visitor::result_type 
  apply_visitor(const Visitor & visitor, Variant & operand);
template<typename BinaryVisitor, typename Variant1, typename Variant2> 
  typename BinaryVisitor::result_type 
  apply_visitor(BinaryVisitor & visitor, Variant1 & operand1, 
                Variant2 & operand2);
template<typename BinaryVisitor, typename Variant1, typename Variant2> 
  typename BinaryVisitor::result_type 
  apply_visitor(const BinaryVisitor & visitor, Variant1 & operand1, 
                Variant2 & operand2);
template<typename Visitor> 
  apply_visitor_delayed_t<Visitor> apply_visitor(Visitor & visitor);

Description

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.
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.)

Returns: 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.
Requires: The given visitor must fulfill the StaticVisitor concept requirements with respect to each of the bounded types of the given variant.
Throws: 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.)