utf8s.Len()

len.go

@@ -0,0 +1,22 @@
+package utf8s
+
+// Len returns the number of bytes in a UTF-8 encoding of this Unicode code point.
+func Len(r rune) int {
+
+	switch {
+	case 127 > r:
+		return 1
+
+	case 0x7FF >= r:
+		return 2
+
+	case 0xFFFF >= r:
+		return 3
+
+	case 0x10FFFF >= r:
+		return 4
+
+	default:
+		return 0
+	}
+}

len_test.go

@@ -0,0 +1,56 @@
+package utf8s
+
+import (
+	"testing"
+)
+
+func TestLen(t *testing.T) {
+
+	tests := []struct{
+		Datum rune
+		Expected int
+	}{
+		{
+			Datum:   'A',
+			Expected: 1,
+		},
+		{
+			Datum:   'r',
+			Expected: 1,
+		},
+		{
+			Datum:   '¡',
+			Expected: 2,
+		},
+		{
+			Datum:   '۵',
+			Expected: 2,
+		},
+		{
+			Datum:   '‱',
+			Expected: 3,
+		},
+		{
+			Datum:   '≡',
+			Expected: 3,
+		},
+		{
+			Datum:   '𐏕',
+			Expected: 4,
+		},
+		{
+			Datum:   '🙂',
+			Expected: 4,
+		},
+	}
+
+
+	for testNumber, test := range tests {
+
+		actual := Len(test.Datum)
+		if expected := test.Expected; expected != actual {
+			t.Errorf("For test #%d, expected %d, but actually got %d.", testNumber, expected, actual)
+			continue
+		}
+	}
+}