C++ Variant type for DBus object path

[Andrejs Hanins <andrejs hanins ubnt com>]

Hi,

        Currently in Glibmm GDBus it seems no straightforward way to dynamically cast VariantBase containing 
some signature with object paths (o) into strictly typed Variant container. I faced the problem when 
interpreting (casting) the result of standard DBus org.freedesktop.DBus.ObjectManager.GetManagedObjects() 
method call which return signature is a{oa{sa{sv}}} (note 'o'). Typed Variant in my code is defined like this:

        Glib::Variant<std::map<Glib::ustring, std::map<Glib::ustring, std::map<Glib::ustring, 
Glib::VariantBase>>>>

but the Glib::VariantBase::cast_dynamic fails with bad_cast, because the type signature of the typed Variant 
is a{sa{sa{sv}}}, thats is, object 'o' is replaced with just 's'.

        My question - is there some ready-to-use type which can be used as a parameter of Variant<> template 
to specify that the Variant holds an object path, not just ordinary string?

        Of course, it is possible to create such a class in the client code like this (pseudo code):

class obj_path_t : public Glib::ustring;

template<>
class Variant<obj_path_t> : public Variant<Glib::ustring>
{
    static const VariantType& variant_type() { return VARIANT_TYPE_OBJECT_PATH; }
};

so that typed Variant looks like this:

        Glib::Variant<std::map<obj_path_t, std::map<Glib::ustring, std::map<Glib::ustring, 
Glib::VariantBase>>>>

and it actually works for me (cast_dynamic is OK), but IMO it should be provided by the Glibmm itself. Did I 
overlook something? Or this is just a missing feature?


BR, Andrey