Given the following class hierarchy:
Legend:
Open Class (o)
Sealed Class (*)
Final Class (x)
classDiagram
class BaseException["BaseException o"]
class AuthException["AuthException *"]
class UnknownException["UnknownException o"]
class AuthServiceException["AuthServiceException o"]
BaseException <|-- AuthException
AuthException <|-- UnknownException: implements
AuthException <|-- AuthServiceException: extends
class AuthResult["AuthResult *"]
class AuthSuccessResult["AuthSuccessResult x"]
class AuthPartialSuccessResult["AuthPartialSuccessResult x"] {
+step1Exception: Step1Exception
+step2Exception: Step2Exception
}
class AuthFailureResult["AuthFailureResult x"] {
+exception: AuthException
}
class Step1Exception["Step1Exception x"]
class Step2Exception["Step2Exception x"]
AuthResult <|-- AuthSuccessResult
AuthResult <|-- AuthPartialSuccessResult
AuthResult <|-- AuthFailureResult
UnknownException <|-- Step1Exception: extends
AuthServiceException <|-- Step2Exception: extends
In base_exception.dart we define an exception hiearchy for which all classes inherit BaseException. From this, we derive AuthException which is sealed and has discrete subtypes, namely UnknownException and AuthServiceException.
In auth_result.dart, we define the result of an Auth operation. The result takes one of three discrete states: a successful result (AuthSuccessResult); a partial success (AuthPartialSuccessResult) where either the first or second step of the operation failed with an AuthException; and a complete failure (AuthFailureResult).
Given a method which performs an Auth operation:
Future<AuthResult> performAuthOperation();We expect the following to work:
final result = await performAuthOperation();
switch (result) {
case AuthSuccessResult _:
print('Success');
case AuthPartialSuccessResult(step1Exception: final exception?) ||
AuthPartialSuccessResult(step2Exception: final exception?) ||
AuthFailureResult(:final exception):
print('Partially failed: $exception');
// For exhaustiveness; should never happen.
case AuthPartialSuccessResult(step1Exception: null, step2Exception: null):
print('Unknown error occurred');
}In the second branch, step1Exception, step2Exception, and exception are all subclasses of AuthException, yet its type cannot be inferred. The Analyzer presents the error:
The variable 'exception' has a different type and/or finality in this branch of the logical-or pattern.
Try declaring the variable pattern with the same type and finality in both branches.dartinconsistent_pattern_variable_logical_or
final result = await performAuthOperation();
switch (result) {
case AuthSuccessResult _:
print('Success');
case AuthPartialSuccessResult(step1Exception: final AuthException exception) ||
AuthPartialSuccessResult(step2Exception: final AuthException exception) ||
AuthFailureResult(:final AuthException exception):
print('Partially failed: $exception');
// For exhaustiveness; should never happen.
case AuthPartialSuccessResult(step1Exception: null, step2Exception: null):
print('Unknown error occurred');
}By explicitly specifying the exception types as AuthException, the analyzer stops complaining.
However, upon compilation, we get a similar error:
bin/sealed_repro.dart:28:71: Error: Variable pattern 'exception' doesn't have the same type or finality in all cases.
case AuthPartialSuccessResult(step1Exception: final AuthException exception) ||
^^^^^^^^^
