override equals and toString for Pair

Author: Jarvan Zhang

lib/src/foundation/pair/pair.dart

@@ -21,6 +21,19 @@ class Pair<F, S> {
   final S second;
 
   const Pair(this.first, this.second);
+  @override
+    bool operator ==(Object other) =>
+        identical(this, other) ||
+        other is Pair<F, S> &&
+            runtimeType == other.runtimeType &&
+            first == other.first &&
+            second == other.second;
+
+    @override
+    int get hashCode => first.hashCode ^ second.hashCode;
+
+    @override
+    String toString() => 'Pair($first, $second)';
 }
 
 /// create pair for given elements first and second.

test/pair/pair_test.dart

@@ -10,5 +10,12 @@ void main() {
       expect("first", result.first);
       expect(1, result.second);
     });
+
+    test("pair equal", () {
+      var pair1 = pairOf("first", 2);
+      var pair2 = pairOf("first", 2);
+
+      assert(pair1 == pair2);
+    });
   });
 }