feat: UI work to facilitate future improvements in midi-into-track-input

tracker/optional_int.go

@@ -0,0 +1,42 @@
+package tracker
+
+type (
+	// OptionalInt tries to follow the same convention as e.g. Int{...} or Bool{...}
+	// Do not confuse with types.OptionalInteger, which you might use as a model,
+	// but don't necessarily have to.
+	OptionalInt struct {
+		optionalIntData
+	}
+
+	optionalIntData interface {
+		Unpack() (int, bool)
+		Value() int
+		Range() intRange
+
+		setValue(int)
+		unsetValue()
+		change(kind string) func()
+	}
+
+	TrackMidiVelIn Model
+)
+
+func (v OptionalInt) Set(value int, present bool) (ok bool) {
+	if !present {
+		v.unsetValue()
+		return true
+	}
+	// TODO: can we deduplicate this by referencing Int{...}.Set(value) ?
+	r := v.Range()
+	if v.Equals(value, present) || value < r.Min || value > r.Max {
+		return false
+	}
+	defer v.change("Set")()
+	v.setValue(value)
+	return true
+}
+
+func (v OptionalInt) Equals(value int, present bool) bool {
+	oldValue, oldPresent := v.Unpack()
+	return value == oldValue && present == oldPresent
+}