Re: [boost] [system] Add noexcept to conform with C++11

Subject: Re: [boost] [system] Add noexcept to conform with C++11
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-12-09 13:21:55

Le 09/12/12 15:03, Beman Dawes a écrit :
> On Sun, Dec 9, 2012 at 5:00 AM, Vicente J. Botet Escriba
> <vicente.botet_at_[hidden]> wrote:
>> Le 08/12/12 21:19, Beman Dawes a écrit :
>>
>>> On Sat, Dec 8, 2012 at 8:42 AM, Vicente J. Botet Escriba
>>> <vicente.botet_at_[hidden]> wrote:
>>>> Hi,
>>>>
>>>> any news on https://svn.boost.org/trac/boost/ticket/7278.
>>>>
>>>> I could add them if you don't have the time now.
>>> Go ahead!
>>>
>>>
>> As the change is a breaking change I would like to update all the libraries
>> at once. I have identified the following dependent libraries: asio,
>> filesystem, thread. Are there other libraries?
> chrono?
>
> We need to contact Chris Kohlhoff to coordinate any asio changes with
> him. I have a vague recollection that he maintains the asio codebase
> elsewhere, so boost trunk is really just a mirror of some other repo.
> But I could be wrong about that.
>
>> Should I introduce the change conditionally so that the users could comeback
>> to the preceding semantics?
>>
>> I was thinking on defining a new BOOST_SYSTEM_NOEXCEPT that the users will
>> use instead of BOOST_NOEXCEPT. The user could define BOOST_SYSTEM_NOEXCEPT
>> as nothing to get the old semantic.
>> Of course as the needed change in the user code is minor, we could also
>> choose the drastic way and add a breaking change respect to the preceding
>> version.
> What happens if a user has built boost libraries without defining
> BOOST_SYSTEM_NOEXCEPT but then compiles his or her own code with
> BOOST_SYSTEM_NOEXCEPT defined, or visa versa? Isn't that an ODR
> violation? Could this result in the generated code for a call to a
> boost.system function being incompatible with the code that was
> generated when the library was built? And wouldn't such a bug be
> particularly insidious because it  might not cause a problem until
> some future date when an error occurred?
>
> That seems a lot worse than the noisy compiler error that will happen
> if user code just broke. How many folks are using a compiler that
> supports C++11 noexcept, have C++11 turned on, and are deriving from
> boost::system_error? Or am I missing other cases where user code would
> break?
Macros to configure the system should be limited to the Boost 
administrator. This could be added in the documentation.

Whether we provide them or not is a question of whether we want to take 
in account the regression or not. If I was a user that had a lot of 
classes inheriting from system classes I would appreciate this macro as 
it give me some time to make the move.
>> Beman up to you to decide.
> I want to hear from others, particularly Chris, before making a decision.
>
>
Sorry, I have committed the BOOST_SYSTEM_NOEXCEPT version 
https://svn.boost.org/trac/boost/changeset/81808.

Of course I can changes any BOOST_SYSTEM_NOEXCEPT by BOOST_NOEXCEPT or 
just change

#ifndef BOOST_SYSTEM_NOEXCEPT
   #define BOOST_SYSTEM_NOEXCEPT BOOST_NOEXCEPT
#endif

by

   #define BOOST_SYSTEM_NOEXCEPT BOOST_NOEXCEPT

Please let me know if I need to do something.
Vicente