пн, 29 апр. 2019 г. в 20:44, Steven Watanabe via Boost
AMDG
On 4/29/19 11:30 AM, Antony Polukhin via Boost wrote:
I've merged a very cool optimization by Nikita Kniazev into the master branch. From now on boost::variant does pointer stealing for recursive variants.
This significantly improves the performance of the variants move constructors.
However if you use a variant variable after the std::move for anything except destruction and assignment then you're getting an UB. Beware!
boost::variant goes to great lengths to prevent exactly this situation. You just broke it. This change is unacceptable. Please revert it. This optimization can be used iff. you have a way to construct a valid object in the rhs.
You can restore the old slow pre-rvalue era behavior by defining BOOST_VARIANT_NO_RECURSIVE_WRAPPER_POINTER_STEALING. -- Best regards, Antony Polukhin