boost::optional<DefaultConstructable>::operator= chooses wrong overload for {}

[mathias@…]

boost::optional<int> op = 5; // creates engaged optional
op = {}; // currently does op = 0;

For most types operator={} assigns from a value-constructed value of that type. That is the behavior of std::experimental::optional but not boost::optional<T>. It chooses the T&& overload. I think the standard avoids it by having the assign-from-T operator= be templated on U instead, which doesn't match {}.

[mathias@…]

Shows the issue. (Compiled with g++6.2 with no extra args)

[akrzemi1]

Already fixed in 1.63