boost::optional<optional<T>&> broken in 1.61.0

[benzejaa@…]

With the new specialization for boost::optional<T&>, there's one use case that's broken now...if T is itself an optional, things are broken.

Diving into optional/detail/optional_reference_spec.hpp it looks like there's some boost::enable_if statements disabling this functionality. Presumably these statements are to differentiate from the copy constructors/assignment above (although I'm not sure why some of the other statements are similarly guarded). However "is_no_optional" is too broad of a guard.

Likely something like !boost::is_same<optional<T&>, typename boost::decay<R>::type> would be a better condition...I'll try it out and update with further info.

[anonymous]

For posterity, here's a reproducer:

#include<boost/optional.hpp>

int main()
{
   boost::optional<int> x;
   boost::optional<boost::optional<int>&> y(x); //compile error
   return 0;
}

[benzejaa@…]

Pull request of fix

​https://github.com/boostorg/optional/pull/18

[benzejaa@…]

Whoops, that patch has a minor typo...hold on, let me generate a fixed one

[benzejaa@…]

Okay same pull request, fixed typo (apparently github lets me just stealthy push --force behind the scenes and updates my pull request automatically...nice!)