Re: [boost] Noexcept

Subject: Re: [boost] Noexcept
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2017-06-19 10:58:15

2017-06-15 1:28 GMT+02:00 Gavin Lambert via Boost <boost_at_[hidden]>:

> On 15/06/2017 07:52, Richard Hodges wrote:
>
>> If developers do not understand RAII, then an afternoon of training can
>> solve that.
>>
>> RAII is the foundation of correct c++. It is the fundamental guarantee of
>> deterministic object state. A program without RAII is not worthy of
>> consideration. The author may as well have used C.
>>
>> Perhaps there is an argument that says that RAII adds overhead to a
>> program’s footprint. If things are that tight, fair enough.
>>
>
> Given that RAII is so fundamental to exception safety, it's surprising
> that there isn't a vocabulary execute-lambda-inside-destructor type (eg.
> "guard") in the STL, to replace cleanup/try-finally style code.
>
> Granted, it's simple to write one yourself, but that seems like a poor
> rationalisation to omit it, especially once lambdas became standard.
>
> I suspect that the lack of such a type is probably a significant reason
> exception-unsafe code ends up surviving -- it's more effort to write RAII
> wrappers for code that you're not really expecting to encounter exceptions
> in, even though you should.

If you allow arbitrary lambdas to be called at the end of the scope, this
itself causes many bugs:
1. They have access to scope variables that might already have been
destroyed when the lambda is executed. It is easy to overlook it. (This is
a no-problem for destructors, because they do not see the context in which
they are called.)
2. People will start calling a potentially throwing lambdas, which may
result in double-exception problem. (This is not a problem in Java-like
languages, where you simple ignore some errors.)

Regards,
&rzej;