Make tables implement equals and hashCode

Fixes #74

moor/lib/src/runtime/structure/table_info.dart

@@ -49,4 +49,16 @@ mixin TableInfo<TableDsl extends Table, D extends DataClass> {
   D map(Map<String, dynamic> data, {String tablePrefix});
 
   TableInfo<TableDsl, D> createAlias(String alias);
+
+  @override
+  bool operator ==(other) {
+    // tables are singleton instances except for aliases
+    if (other is TableInfo) {
+      return other.runtimeType == runtimeType && other.$tableName == $tableName;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode => $mrjf($mrjc(runtimeType.hashCode, $tableName.hashCode));
 }

moor/test/tables_test.dart

@@ -0,0 +1,35 @@
+import 'package:test_api/test_api.dart';
+
+import 'data/tables/todos.dart';
+import 'data/utils/mocks.dart';
+
+void main() {
+  TodoDb db;
+  MockExecutor executor;
+
+  setUp(() {
+    executor = MockExecutor();
+    db = TodoDb(executor);
+  });
+
+  test('aliased tables implement equals correctly', () {
+    final first = db.users;
+    final aliasA = db.alias(db.users, 'a');
+    final anotherA = db.alias(db.categories, 'a');
+
+    expect(first == aliasA, isFalse);
+    // ignore: unrelated_type_equality_checks
+    expect(anotherA == aliasA, isFalse);
+    expect(aliasA == db.alias(db.users, 'a'), isTrue);
+  });
+
+  test('aliased table implement hashCode correctly', () {
+    final first = db.users;
+    final aliasA = db.alias(db.users, 'a');
+    final anotherA = db.alias(db.categories, 'a');
+
+    expect(first.hashCode == aliasA.hashCode, isFalse);
+    expect(anotherA.hashCode == aliasA.hashCode, isFalse);
+    expect(aliasA.hashCode == db.alias(db.users, 'a').hashCode, isTrue);
+  });
+}