Apply the specified visitor to this modifiable variant by passing the value this variant currently holds to the visitor object's operator(). This method does not return a value. If this variant is unset, a default constructed bslmf::Nil is passed to the visitor. Note that this method is selected only if the template parameter type VISITOR does not define a typedef of ResultType in its public interface. Also note that this method is defined inline to work around a Windows compiler bug with SFINAE functions.
Declared in <bdlb_variant.h>
template<class VISITOR>
void
apply(VISITOR& visitor)
requires Variant_ReturnValueHelper<VISITOR>::value == 0;