[#294] object: Implement Cmp() function for ID struct

Signed-off-by: Alexander Chuprov <a.chuprov@yadro.com>

object/id/id.go

@@ -1,6 +1,7 @@
 package oid
 
 import (
+	"bytes"
 	"crypto/ecdsa"
 	"crypto/sha256"
 	"fmt"
@@ -167,3 +168,9 @@ func (id *ID) UnmarshalJSON(data []byte) error {
 
 	return nil
 }
+
+// Cmp returns an integer comparing two base58 encoded object ID lexicographically.
+// The result will be 0 if a == b, -1 if a < b, and +1 if a > b.
+func (id ID) Cmp(id2 ID) int {
+	return bytes.Compare([]byte(id.EncodeToString()), []byte(id2.EncodeToString()))
+}

object/id/id_test.go

@@ -1,8 +1,10 @@
 package oid
 
 import (
+	"bytes"
 	"crypto/rand"
 	"crypto/sha256"
+	"slices"
 	"strconv"
 	"testing"
 
@@ -180,3 +182,18 @@ func TestID_Encode(t *testing.T) {
 		require.Equal(t, emptyID, id.EncodeToString())
 	})
 }
+
+func TestID__Cmp(t *testing.T) {
+	id1 := randID(t)
+	id2 := randID(t)
+	id3 := randID(t)
+
+	arr := []ID{id1, id2, id3}
+
+	slices.SortFunc(arr, ID.Cmp)
+	for i := 1; i < len(arr); i++ {
+		if bytes.Compare([]byte(arr[i-1].EncodeToString()), []byte(arr[i].EncodeToString())) > 0 {
+			t.Fatalf("arrays are not sorted correctly")
+		}
+	}
+}