Role of msgFuncKeepGate?

Questions
1

I see one can set this flag which by default is false to true and that will rebuild the msgFunc of the SynthDef, e.g.

SynthDescLib.global[\default].msgFuncKeepGate = true

but I can’t figure out what’s different with that flag on. The controls, at least for the default synthdef include gate for either setting… So when is that msgFuncKeepGate actually effective? I see the actual msgFunc is changed. With keep… true

SynthDescLib.global[\default].msgFunc.cs

-> #{ arg out, freq, amp, pan, gate;
	var	x3E7438F4 = Array.new(10);
	out !? { x3E7438F4.add('out').add(out) };
	freq !? { x3E7438F4.add('freq').add(freq) };
	amp !? { x3E7438F4.add('amp').add(amp) };
	pan !? { x3E7438F4.add('pan').add(pan) };
	gate !? { x3E7438F4.add('gate').add(gate) };
	x3E7438F4
	
SynthDescLib.global[\default].msgFuncKeepGate = false
SynthDescLib.global[\default].msgFunc.cs
	
-> #{ arg out, freq, amp, pan;
	var	x3E7438F4 = Array.new(8);
	out !? { x3E7438F4.add('out').add(out) };
	freq !? { x3E7438F4.add('freq').add(freq) };
	amp !? { x3E7438F4.add('amp').add(amp) };
	pan !? { x3E7438F4.add('pan').add(pan) };
	x3E7438F4

However, because Event.default has args: #[\freq, \amp, \pan, \trig], and Event \set looks at ~args size before deciding whether to look at ~msgFunc, it’s actually a bit tricky to test this:

y = Synth(\default)
(type: \set, id: y.nodeID, gate: 0, args: []).play // resets freq, doesn't turn off
(type: \set, id: y.nodeID, gate: 0, args: [\gate]).play // turns off

SynthDescLib.global[\default].msgFuncKeepGate = true 
y = Synth(\default)

(type: \set, id: y.nodeID, gate: 0, args: []).play // now resets freq AND turns off

So clearly the ~msgFunc is “gate-capable” in the latter case (after msgFuncKeepGate is turned on) and it does make a difference in Event-set use… but still I don’t get it why the frequency (still) resets with keep true… (I guess it’s because there are no default values in the msgFunc. Still the freq gets set to some 260 Hz or so…)

2

A convention, illustrated in the \default SynthDef, is to set a positive default for gate. If the default is positive, then it’s not necessary to send a gate value – so we save a little CPU time and don’t put it in the message.

But you might want to send the gate value in some cases, so the option is there. But it’s only an option.

hjh