Re: [Vala] Questions about structs: printing, copying, ArrayList<StructType?>

[Evan Nemerson <evan coeus-group com>]

On Mon, 2011-08-22 at 08:36 -0700, bsquared wrote:
> I ran into a couple of issues regarding structs.
>
> 1. When using a struct from a pkg, as opposed to one of my creation,
> an error is raised in the c code when attempting to access the
> "built-in" to_string() method for an element.
>
>                   Context.State state = ctx.get_state();
>                   print (state.to_string());
>
> /.../Source/vala/pulse-device-chooser/src/main.t c:160:47: error:
> ‘PA_CONTEXT_TYPE_STATE’ undeclared (first use in this function)

Looks like a missing CCode annotation in the VAPI. Depending on whether
Context.State has a GType

[CCode (type_id = "pa_context_state_get_type ()")]

or

[CCode (has_type_id = false)]

> 2. What is the correct method to copy a struct?  Attempting to copy
> struct by assignment to variable, or Memory.copy causes "undefined
> reference to `pulse_audio_sink_info_copy'" errors in c code.

There is no generic way to copy a struct. It depends on the library.
There may even be no way to copy, in which case you would likely need to
make judicious use of the "unowned" keyword.

> where i & si are type PulseAudio.SinkInfo
>
>                 context.get_sink_info_by_index (index, (context, i, eol) => {
>                         Memory.copy(&i, &si, sizeof(SinkInfo));
>                         si = i;
>                 });
>
>
>
> 3. Attempting to box struct from pkg in an ArrayList causes an error
> in c code similar to question 1.
> Gee.ArrayList<SinkInfo?> sink_info = new Gee.ArrayList<SinkInfo?>();
>
> main.c:643:31: error: ‘PULSE_AUDIO_TYPE_SINK_INFO’ undeclared (first
> use in this function)

The solution is the same as above... either specify the correct type id
or set has_type_id = false for SinkInfo.