Thiago Macieira thiago at
Thu May 13 06:31:53 PDT 2010

Em Quinta-feira 13. Maio 2010, às 13.17.04, David Zeuthen escreveu:
> > But I don't like giving people the ability to search for an interface.
> > That will lead to bad client code instead.
> [Citation needed] (I, for one, don't agree with your assertion. But,
> hey, I could be convinced if there's a good example....)
> Btw, if we wanted to make things more complicated, we *could* replace
> Lennart's interface string with a D-Bus Match Rule since it is already
> designed to match things. But I think that's a bit too much to require
> each client and/or binding to implement support for that. But it _is_
> more generic! :-)


For the past 4 years, I've been telling people that they have to know the 
interface that they are talking to, including which objects it may be found 
in. They must not scan running applications to find if an interface is present. 

Or, alternatively, they add a method call to return a list of paths. But 
that's exactly my recommendation looked from another angle: there's a well-
known interface, at a well-known path, that returns information you want.

But in this case, it's for a specific purpose.

Adding a method that returns all object paths that implement a given interface 
is, in my opinion, a bad idea. It will lead to people writing client code that 
scans applications for an interface, instead of thinking their problem 
through. Worse, it may lead to people scanning ALL running programs for 
existing instances of an interface. And there's an inherent race condition 
involved: the object may disappear right after the call.

So, in summary: I like the splitting of dynamic information (the list of sub-
objects) from mostly-static information, the interface list.

If you want to take this one step further, you may also want to decouple the 
many interfaces from one another. Add a method to 
org.freedesktop.DBus.Introspectable that returns a list of strings, one with 
the XML of each interface, instead of one big string with all interfaces 

Thiago Macieira - thiago (AT) - thiago (AT)
  Senior Product Manager - Nokia, Qt Development Frameworks
      PGP/GPG: 0x6EF45358; fingerprint:
      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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