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Smart pointer with custom deleter with 'using pointer = <pointer type>'

To manage libmagic's `magic_t` aka `magic_set*` cookie with a `unique_ptr` and a custom deleter in a RAII wrapper, I have:

    struct MagicDeleter {

        // magic_t is already a pointer (magic_set*)
        using pointer = magic_t;

        void operator()(magic_t cookie) noexcept {
            if (cookie) magic_close(cookie);
        }
    };

    using unique_magic_ptr = std::unique_ptr<magic_t, MagicDeleter>;

and then initialize and use it like:

    m_cookie {unique_magic_ptr(magic_open(MAGIC_MIME_TYPE))};

    magic_load(m_cookie.get(), nullptr);

This works fine and `valgrind` says all is good.

Since `magic_t` is a pointer already, and I don't think I can or should use `magic_set`, without `using pointer = magic_t`, I get errors like:

 > cannot convert argument of incomplete type 'magic_t' (aka 'magic_set *') to 'pointer' (aka 'magic_set **') for 1st argument

Do I understand correctly, that `using pointer = magic_t` informs `unique_ptr` "indirectly" via the deleter, that the pointer to be managed actually is `magic_t`?
Is this a valid way to do?