Re: [boost] [result_of] Allow result_of to work with C++11 lambdas

Subject: Re: [boost] [result_of] Allow result_of to work with C++11 lambdas
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-04-21 03:04:37

Le 20/04/13 23:25, Nathan Crookston a écrit :
> Hi Daniel,
>
> Daniel Walker wrote:
>
>> Nathan Crookston wrote:
>>> I just wanted to ping on this; see if someone's had time to review the
>>> patch.  I failed to mention that the same parts of the full test suite
>>> passes on VC10 before and after the patch, so there's some assurance that
>>> it's correct.
>> OK, I finally had a chance to look at the patch. The implementation is
>> fine, but the configuration, documentation and tests allow/imply that
>> BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK is enabled by default on
>> certain compilers. I believe we should not stealthily change the default
>> behavior. It seems to me that the migration path we adopted years ago
>> should remain in place: the default behavior of boost:result_of will only
>> change if your compile supports N3276, in which case you will get the full
>> decltype implementation.
>>
>> I think it would be best to introduce this functionality as a third
>> option; i.e. one that the user opts into by explicitly defining
>> BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK. (That's a good name for the
>> macro, BTW.) If you could update the patch, I'd be glad to apply it.
>>
> Thanks for looking over the patch!  I'd be happy to make the change, if
> that means getting the functionality into boost.  However, I think that the
> decltype fallback should be enabled at least for those compilers which have
> both a lacking decltype implementation and C++11 lambdas.  This doesn't
> change the migration path, of course -- as N3276 is implemented in more
> compilers, more compilers will use the straight (standards conforming)
> decltype implementation.
>
> I don't think there are typical situations where someone using lambda
> functions would *not* want boost::result_of to work for it.  However, I'll
> submit a patch updated as you request in a few days, unless I and/or others
> can help change your mind. ;)
>
Could, defining BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK by 
default on these compilers, result on a regression on these compilers?

If not it should be done as it allows to take care of more cases.

Do we know of some regression cases?

Vicente