Re: Exceptions as smart pointers

"Sergey P. Derevyago" <>
Tue, 26 Aug 2008 09:46:03 CST
David Abrahams wrote:

Then that's still not very useful, because the dtor might be called from
inside a catch block where the programmer needs non-throwing operations,
and in_stack_unwinding would be false.

Could you show the code, please?

I don't see how. The information about what is "safe" is not encoded in
the program text; it's a function of the semantics the programmer is
trying to achieve.

The point is that if in_stack_unwinding==true then an exception from
the destructor *shall* lead to terminate(). No guess, this is a strong

Time to give your definition of "safe," then ;-)

Let's put it another way: if in_stack_unwinding==true then it's UNSAFE
to throw exceptions.

Okay. I *think* the cost of copying exceptions should not be a major
concern. Have you profiled?

I agree, no need to profile :)
    But it's always _safe_ to copy sh_ptr<Exception>() object: we have
nothrow guarantee here.

On the contrary, Exception copy constructor does
really throw exceptions so its copying is expensive and can lead to

Depends on what Exception is, neh?

Non-trivial Exception classes tend to be unsafe.
    So it really makes sense to use sh_ptr<Exception> object rather than
fight all of the dirty details (of nothrow guarantee).

     3. It's really easy to create the chains of the nested Exception


And it was the root of the problem!

    At the time, I tried to get portable and easy-to-use C++ exception
traces that somehow resemble my Java code. The direct solution is

     4. Having recatchException() function you can use the following
uniform exception handler in almost all of the places:

void f()
 try {
     // ...
     // ...

 catch (...) {
       throw newException(_FLINE_, "Problems in f()",
         recatchException(mp, _FLINE_));

I still don't understand what recatchException is supposed to do.
What's mp above?

shException recatchException(mem_pool& mp, const FileLine& location)
  try { throw; }
  catch (shException she) {
        return she;
  catch (const std::exception& se) {
        return newStdExternException(mp, location, se.what(),
  catch (...) {
        return newUnknExternException(mp, location, "Unknown exception");

    You can use the following link to see the details:
          With all respect, Sergey.
          mailto : ders at

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