On Mon, Feb 3, 2025 at 11:14 AM Andrey Semashev wrote:
>
>
> It is not. A forward declaration would suffice.


But I'll be need forward declarations for other stuff like "std::less"
and "std::allocator":

    namespace std {
        template<class T> class less;
        template<class T> class allocator;
        template< class Key, class Compare = less<Key>, class
Allocator = allocator<Key> > class set;
    }

    typedef std::set<unsigned> IndexSet;