[Vala] How to extend IOStream in Vala?

[Paul Jakma <paul jakma org>]

Hi,

I want to extend IOStream, to create a memory channel based IO stream, by 
wrapping around some modified Memory{In,Out}putStreams. However, it 
doesn't seem to be possible, because the input_stream and output_stream 
properties of IOStream are read-only. I get this warning if I try to set 
them from my extending class:

MemoryIOStream.vala:44.5-44.23: error: Property 
`GLib.IOStream.input_stream' is read-only

If I try to define these fields in my extending class, i.e.:

  public InputStream input_stream { public get; private set; }
  public OutputStream output_stream { public get; private set; }

I get a warning that I'm hiding the visibility of the inherited 
property[1]:

warning: MemoryIOStream.output_stream hides inherited property 
`GLib.IOStream.output_stream'. Use the `new' keyword if hiding was 
intentional

and then, if I use Object (input_stream : ..., output_stream ...) to set 
these properties I get a runtime error from GLib:

(process:16186): GLib-GObject-WARNING **: g_object_newv: property 
`input-stream' of object class `MemoryIOStream' is not writable

(process:16186): GLib-GObject-WARNING **: g_object_newv: property 
`output-stream' of object class `MemoryIOStream' is not writable

So clearly, it's the base class property being invoked (the code is 
accessing via the base type of IOStream). OTOH, if I set them with 
'output_stream = ....', then I get a crash as the properties are never 
set, if the object is invoked via the IOStream type. If I add the 'new' 
keyword, it gets rid of the hiding warning, but doesn't make any other 
discernible difference.

My problem then is that I don't see how I can extend IOStream reliably, 
when there doesn't seem to be any way to set or fully override the base 
class's properties. Is there any way? Or does the Vala VAPI for IOStream 
need to be modified to allow the properties to be set by child classes? Or 
is that not even possible with extensions of classes and properties?

1. Incidentally, I couldn't find the 'new' modifier for properties 
documented anywhere.

regards,
--
Paul Jakma  paul jakma org  twitter: @pjakma  PGP: 64A2FF6A
Fortune:
The only thing that experience teaches us is that experience teaches us nothing.
                -- Andre Maurois (Emile Herzog)