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

Section: 15.5.5.12 [res.on.exception.handling] Status: TC1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2016-02-10

Priority: Not Prioritized

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Discussion:

Section 15.5.5.12 [res.on.exception.handling] states:

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

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

For example, this would not compile if ios_base::failure::~failure had 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 15.5.5.12 [res.on.exception.handling] from:

     "may strengthen the exception-specification for a function"

to:

     "may strengthen the exception-specification for a non-virtual function".