Re: [Dbus-cxx-users] MessageAppendIterator::operator<< begin called instead of overload defined in global namespace

[Robert M. <rmi...@sy...>]

Interesting observation, I'm guessing that what's going on is because of
how the includes are being parsed, the second parameter is being compiled
as a separate compilation unit or something.  Could you attach the sources
that you've been using to test this?  I think I understand what you're
saying but I want to be sure.

One possible solution would be to not use operator<< and operator>> in
order to do serialization/deserialization.  Personally, I'm not a fan of
overloading operators, but it works so I haven't done anything with it.  I
almost think that maybe the best solution here would be to re-design how
the messages are built up, so that it would be possible to add in different
types of appenders into the system - as it stands right now, defining
custom types is rather convoluted(and apparently prone to errors).

-Robert Middleton


On Mon, Nov 18, 2013 at 9:03 AM, <emm...@or...> wrote:

> Hello,
>
> Lately, I have been playing around with DBus-cxx and user-defiend types.
>
> When working with custom types in DBus-cxx, I found that
> MethodProxy::operator() will call the template member operator<< in
> MessageAppendIterator instead of the user-defined overload in the global
> namespace *starting*with*the*second*method*parameter*.
> MessageAppendIterator::operator<< in turn attempts to call the
> MessageAppendIterator::append overload which does not exist and raises a
> compiler error. This happens at least with GCC 4.6.3
>
> The bug can be reproduced by slightly modifying the time client/server
> example in examples/basics/types. Just add *two* dummy parameters of type
> struct timeval to the now() method to trigger this.
>
> As a fix, I propose that MessageAppendIterator::operator<< be modified to
> delegate its implementation to a template struct with a static append()
> method. The user would then have to specialize this struct instead of
> defining his/her own operator<< for custom types. Lazy instantiation of
> operator<< would ensure that the appropriate specialization is used.
>
> This would also have the benefit of allowing one partial specialization to
> be used for a broad range of types. As an example, I'm using this to
> automatically serialize introspectable types (e.g. through
> boost::enable_if<is_introspectable<T>>::type).
>
> Please see attached patch for the proposed solution. This is a patch
> against dbus-cxx 0.8.0.
>
> By the way, it would also be nice if deserialization also worked that way.
> Maybe serialization, deserialization and signature could all rely on a
> single traits structure as a default?
>
> Regards,
>
> --
> Emmanuel
>
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