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From: Ian Clifton <ian.clifton@chem.ox.ac.uk>
Newsgroups: comp.lang.ada
Subject: Re: Empty arrays & libdbusada
Date: Wed, 29 Jun 2016 22:49:53 +0100
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Xref: news.eternal-september.org comp.lang.ada:30976
Date: 2016-06-29T22:49:53+01:00
List-Id: <comp.lang.ada>

Reto Buerki <reet@codelabs.ch> writes:

> On 2016-06-28, Ian Clifton <ian.clifton@chem.ox.ac.uk> wrote:
>> I’m trying to learn a bit about controlling programs through D-bus. I
>> can make things happen with the “D-feet” tool, calling methods in
>> ork.gtk.Actions and org.gtk.Application, supplying empty arrays (notated
>> as “[]”) for un‐needed parameters. But when I try to do the equivalent
>> in Ada code using libdbusada, I hit a snag—libdbusada doesn’t seem to be
>> able to handle empty arrays. Does anyone know of a way round this?
>> Thanks,
>
> Can you please provide a concrete example of what you are trying to do?
> What happens if you just remove the empty array arguments?
>
Thanks for replying. At the moment I’m trying to control the play‐back
of a CD using the “Sound Juicer” application on Debian Linux. The
application exposes the “org.gtk.Actions” interface through D-Bus. Using
D-feet, I can toggle playback by calling the “Activate” method with
three arguments:

'play', [], []

i.e. the string 'play' followed by two empty arrays to mark the places
of un‐needed parameters. 

If I omit these placeholders in my Ada code I get:

   raised D_BUS.D_BUS_ERROR : Type of message, '(s)', does not match
   expected type '(sava{sv})'

If I supply empty arrays (uninitialised
D_Bus.Arguments.Containers.Array_Type variables) I get:

   raised D_BUS.D_BUS_ERROR : Serialization error: Array is empty

and if I put either empty strings or nonsense strings into containers of
the expected type, my method calls seem to be passed without error but
are ignored by the application.
-- 
Ian ◎