Attempting to return a fundamental type from a signal in the example below triggers the following warning:

(process:24588): GLib-GObject-CRITICAL **: g_value_take_object: assertion 'G_VALUE_HOLDS_OBJECT (value)' failed

class Klass
{
	public signal Klass emit ();

	public Klass ()
	{
		this.emit.connect (() => {
			return new Klass ();
		});
	}
}

void main ()
{
	var one = new Klass ();
	var two = one.emit ();
}

The code runs fine if Klass is modified to inherit from Object.

Note also that the Vala tutorial and all documentation I can find claims that signals are not supported except for types that derive from Object, which this example shows to be false.