Re: [boost] [C++11] If you have an old class with a throwing destructor...

Subject: Re: [boost] [C++11] If you have an old class with a throwing destructor...
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2013-09-16 17:15:19

On 16 Sep 2013 at 16:47, Eric Niebler wrote:

> Sure. And then? Don't say, "Quietly swallow the exception." Something
> Very Bad has happened. Ignoring it inevitably leads to Something Worse
> (like data corruption, security vulnerabilities, etc). The only sensible
> option is to terminate, which is why the language semantics are what
> they are. The OP's suggestion to litter destructors with try/catch is
> misguided. That's no way to build reliable systems.

I agree that if your program has entered undefined state, you need to 
fatal exit.

Fatal exit != immediate std::terminate() though. There's plenty of 
very useful things you can do before you die such as flush buffers, 
kick out memory maps, dump a trace file etc.

Regarding the other comments about "keeping destructors simple enough 
they never throw", sure I agree that if a C++ expert designed and 
wrote all the code then throws from destructors are likely to not 
occur. However in the real world destructors call third party code 
and who knows what they could throw. The truth is that in real world 
code written by non experts you have to assume that every single line 
of C++ can *always* throw, unless it is a function marked noexcept or 
it is a function marked extern "C" (and even then some compilers 
allow C++ exceptions to traverse C code).

I therefore return to my original statement that wrapping destructors 
in try...catch is both useful and wise. Note I did not state that 
fatal exit isn't the wisest choice if a destructor does throw. Unless 
you're bothering to universally write restartable destructors, and 
far more importantly to bear the maintenance burden of doing so and 
training in staff to do so, fatal exit on destructor throw is the 
best course of action.

Niall

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