initial commit

lib/foundation/res.dart

@@ -0,0 +1,36 @@
+class Res<T> {
+  /// error info
+  final String? errorMessage;
+
+  /// data
+  final T? _data;
+
+  /// is there an error
+  bool get error => errorMessage != null;
+
+  /// whether succeed
+  bool get success => !error;
+
+  /// data
+  T get data => _data ?? (throw Exception(errorMessage));
+
+  /// get data, or null if there is an error
+  T? get dataOrNull => _data;
+
+  final dynamic subData;
+
+  @override
+  String toString() => _data.toString();
+
+  Res.fromErrorRes(Res another, {this.subData})
+      : _data = null,
+        errorMessage = another.errorMessage;
+
+  /// network result
+  const Res(this._data, {this.errorMessage, this.subData});
+
+  const Res.error(String err)
+      : _data = null,
+        subData = null,
+        errorMessage = err;
+}