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Function apply_visitor
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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.)

Last revised: , at GMTCopyright © 2002, 2003 Eric Friedman, Itay Maman