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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.

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