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119. Should virtual functions be allowed to strengthen the exception specification?

Section: 16.4.6.14[res.on.exception.handling]Status:TC1Submitter: Judy WardOpened: 1998-12-15Last modified: 2016-01-28

Priority:Not Prioritized

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Discussion:

Section 16.4.6.14[res.on.exception.handling] states:

"An implementation may strengthen the exception-specificationfor a function by removing listed exceptions."

The problem is that if an implementation is allowed to do this forvirtual functions, then a library user cannot write a class thatportably derives from that class.

For example, this would not compile if ios_base::failure::~failurehad an empty exception specification:

#include <ios>#include <string>class D : public std::ios_base::failure {public:        D(const std::string&);        ~D(); // error - exception specification must be compatible with               // overridden virtual function ios_base::failure::~failure()};

Proposed resolution:

Change Section 16.4.6.14[res.on.exception.handling] from:

     "may strengthen theexception-specification for a function"

to:

     "may strengthen theexception-specification for a non-virtual function".