[Bug libstdc++/90220] std::any_cast misbehaves for function and array types

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90220

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Thu May 23 14:18:13 2019
New Revision: 271558

URL: https://gcc.gnu.org/viewcvs?rev=271558&root=gcc&view=rev
Log:
PR libstdc++/90220 fix experimental::any_cast for non-object types

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.

Backport from mainline
2019-05-23  Jonathan Wakely  <jwakely@redhat.com>

        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.

Modified:
    branches/gcc-9-branch/libstdc++-v3/ChangeLog
    branches/gcc-9-branch/libstdc++-v3/include/experimental/any
   
branches/gcc-9-branch/libstdc++-v3/testsuite/experimental/any/misc/any_cast.cc