refactor: implement Order and Pattern types: slices returning default values for out of bound indices

pattern.go

@@ -0,0 +1,21 @@
+package sointu
+
+// Pattern represents a single pattern of note, in practice just a slice of bytes,
+// but provides convenience functions that return 1 values (hold) for indices out of
+// bounds of the array, and functions to increase the size of the slice only by
+// necessary amount when a new item is added, filling the unused slots with 1s.
+type Pattern []byte
+
+func (s Pattern) Get(index int) byte {
+	if index < 0 || index >= len(s) {
+		return 1
+	}
+	return s[index]
+}
+
+func (s *Pattern) Set(index int, value byte) {
+	for len(*s) <= index {
+		*s = append(*s, 1)
+	}
+	(*s)[index] = value
+}