feat: add Compare function (#163)

* feat: add Compare function

* fix comment

util.go

@@ -5,6 +5,7 @@
 package uuid
 
 import (
+	"bytes"
 	"io"
 )
 
@@ -41,3 +42,8 @@ func xtob(x1, x2 byte) (byte, bool) {
 	b2 := xvalues[x2]
 	return (b1 << 4) | b2, b1 != 255 && b2 != 255
 }
+
+// Compare returns an integer comparing two uuids lexicographically. The result will be 0 if a == b, -1 if a < b, and +1 if a > b.
+func Compare(a, b UUID) int {
+	return bytes.Compare(a[:], b[:])
+}

uuid_test.go

@@ -918,10 +918,10 @@ func TestVersion7MonotonicityStrict(t *testing.T) {
 	defer SetRand(nil)
 
 	length := 100000 // > 3906
-	u1 := Must(NewV7()).String()
+	u1 := Must(NewV7())
 	for i := 0; i < length; i++ {
-		u2 := Must(NewV7()).String()
-		if u2 <= u1 {
+		u2 := Must(NewV7())
+		if Compare(u1, u2) >= 0 {
 			t.Errorf("monotonicity failed at #%d: %s(next) < %s(before)", i, u2, u1)
 			break
 		}