Output login errors to user

lib/utility.dart

@@ -0,0 +1,70 @@
+/// Utility class that simplifies handling errors.
+///
+/// Return a [Result] from a function to indicate success or failure.
+///
+/// A [Result] is either an [Ok] with a value of type [T]
+/// or an [Err] with an [Exception].
+///
+/// Use [Result.ok] to create a successful result with a value of type [T].
+/// Use [Result.error] to create an error result with an [Exception].
+///
+/// Evaluate the result using a switch statement:
+/// ```dart
+/// switch (result) {
+///   case Ok(): {
+///     print(result.value);
+///   }
+///   case Error(): {
+///     print(result.error);
+///   }
+/// }
+/// ```
+sealed class Result<T> {
+  const Result();
+
+  /// Creates a successful [Result], completed with the specified [value].
+  const factory Result.ok(T value) = Ok._;
+
+  /// Creates an error [Result], completed with the specified [error].
+  const factory Result.error(Exception error) = Err._;
+
+  bool isOk() {
+    return this is Ok;
+  }
+
+  T value() {
+    Ok<T> ok = this as Ok<T>;
+    return ok._value;
+  }
+
+  bool isErr() {
+    return this is Err;
+  }
+
+  Exception error() {
+    Err<T> err = this as Err<T>;
+    return err._error;
+  }
+}
+
+/// A successful [Result] with a returned [value].
+final class Ok<T> extends Result<T> {
+  const Ok._(this._value);
+
+  /// The returned value of this result.
+  final T _value;
+
+  @override
+  String toString() => 'Result<$T>.ok($_value)';
+}
+
+/// An error [Result] with a resulting [error].
+final class Err<T> extends Result<T> {
+  const Err._(this._error);
+
+  /// The resulting error of this result.
+  final Exception _error;
+
+  @override
+  String toString() => 'Result<$T>.error($_error)';
+}