Re: new type traits

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2020-10-03 09:34:44

On 10/3/20 12:30 PM, Andrey Semashev wrote:
> On 10/3/20 11:53 AM, Gero Peterhoff via Boost wrote:
>> Am 12.09.20 um 16:15 schrieb Andrey Semashev via Boost:
>>> Given that Boost.TypeTraits are not equivalent in some instances to 
>>> std type traits, I don't think we're going to remove them any time 
>>> soon. At least, I would be opposed to such a move.
>>>
>>> You can opportunistically use std type traits and fallback to 
>>> Boost.TypeTraits in some simple cases, but that doesn't really make 
>>> much sense in Boost since that doesn't remove the dependency on 
>>> Boost.TypeTraits and requires workarounds in cases when the type 
>>> traits don't match.
>>>
>>> Also, we normally don't include all-in-one headers like 
>>> <boost/type_traits.hpp> because that brings way more code than 
>>> necessary. This is one of the drawbacks of <type_traits> and one of 
>>> the reasons to use Boost.TypeTraits, actually.
>>
>> - Is there an overview/documentation which Boost.TypeTraits differ 
>> from the standard?
> 
> I haven't seen an overview. But you could read Boost.TypeTraits docs and 
> compare it to the standard to see if there is a difference. Some 
> differences are not documented, I think, like support for 128-bit 
> integers for example.

I should add that in some cases Boost.TypeTraits work around bugs in the 
standard type traits, which is also not documented. For example, 
std::alignment_of would give incorrect result for 64-bit types on 32-bit 
targets and boost::alignment_of works as expected.

>> - Would it make sense to only keep these different/additional 
>> Boost.TypeTraits and remove the standard-compliant ones?
> 
> IMO, no, because there are C++03 libraries and there are no standard 
> type traits in C++03.