Re: The new Boost 17.0.0

From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2020-12-02 18:45:50

On 12/2/2020 6:07 AM, Peter Dimov via Boost wrote:
> Alexander Grund wrote:
> 
>> IMO it would be enough on a cost-benefit ratio to go to C++11 by 
>> basically banning the use of MPL in Boost (the single-worst offender 
>> on compile times) and reducing the use of type_traits to the absolute 
>> minimum. Those 2 are (transitively) in the largest chunk of boost 
>> libraries and hence hit hard on compiletimes.
> 
> What is the problem with TypeTraits?

More than that, many of the standard's type traits are inferior due to 
their cop-out requirements.  I suspect that if compilers actually 
verified those requirements, almost every significant program that used 
them would be ill-formed.  E.g. boost::is_constructible<T, Args...> vs. 
std::is_constructible<T, Args...>.  Both effectively test:

T t(std::declval<Args>()...);

which passes rvalue or lvalue reference types.  Boost's requires T to be 
a complete type.  The standard's requires T *and* all types in Args to 
be complete types.  The standard's type traits are rife with these kinds 
of overzealous requirements.