[Request] non-void signals

[GeopJr]

Could the signal macro support non-void signals?

Use case:
I'm emitting a singal from a child widget to call another function from the parent and want it to return a bool if it succeeded or not

(exact use case: A widget has a button and a clicked signal. The parent connects to the signal that provides the hash function to copy in string (e.g. "MD5"), the parent then copies it to clipboard and should return a bool to the widget if it succeeded or not so the button displays the correct feedback icon (:heavy_check_mark: or :x:))

[hugopl]

You mean: Support signal return values?

Meanwhile it doesn't support, but yes, it's possible to have this.

First step is to let the signal macro register a signal with a return value, so we can inform to GObject the right GType used for the return type at:

https://github.com/hugopl/gi-crystal/blob/main/src/bindings/g_object/object.cr#L596

Then we also need to register a GObject::SignalAcumulator callback.

I never used (or remember to had used) signals with return values, so I would need to do some experiments in libtest to first see it working in C, to later change the macro to let it work in Crystal.

[GeopJr]

You mean: Support signal return values?

Yes!

I never used (or remember to had used) signals with return values

FWIW, there's quite a few in GTK, here's some: Gtk::ComboBox::PopdownSignal, Gdk::Surface::EventSignal, Gtk::SpinButton::InputSignal

[hugopl]

Hmmm, this issue is easier than I expected to implement, it's just a matter of using

void
g_signal_emitv (
  const GValue* instance_and_params,
  guint signal_id,
  GQuark detail,
  GValue* return_value
)

to emit signals when there's a return value, then get the data from this GValue.

I'll kept this issue in mind when reworking the signals stuff on GICrystal to avoid object leaks.