This corresponds to the fixes done for std::any_cast, but has to be done
without if-constexpr. The dummy specialization of _Manager_internal<_Op>
is used to avoid instantiating the real _Manager_internal<T>::_S_manage
function just to compare its address.
PR libstdc++/90220
* include/experimental/any (__any_caster): Constrain to only be
callable for object types. Use remove_cv_t instead of decay_t.
If the type decays or isn't copy constructible, compare the manager
function to a dummy specialization.
(__any_caster): Add overload constrained for non-object types.
(any::_Manager_internal<_Op>): Add dummy specialization.
* testsuite/experimental/any/misc/any_cast.cc: Test function types
and array types.
From-SVN: r271556
