scaffolding around try{}block #noexcept

[[ARM]] P358 says that all local non-static objects on the current call stack fully constructed since start of the try-block are “registered” for stack unwinding. The registration is fine-grained in terms of partial destruction —

  • for any array with 3 out of 9 objects fully constructed, the stack unwinding would only destruct those 3
  • for a half constructed composite object with sub-objects, all constructed sub-objects will be destructed
  • Any half-constructed object is not registered since the dtor would be unsafe.

I guess this registration is an overhead at run time.

For the stack objects created in a noexcept function, this “registration” is not required, so compiler may or may not call their destructors.

— in http://www.stroustrup.com/C++11FAQ.html#noexcept Stroustrup hints at the  scaffolding

  • noexcept is a efficiency feature — widely ans systematically used in standard library to improve performance
  • noexcept is crude and “very efficient”
  • dtor may not be invoked upon stack unwinding
  • stack unwinding may not happen at all

 

 

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