如何从Dart（Dartz）中的任一类型轻松提取Left或Right
问题内容：
我希望从返回类型的方法中轻松提取值Either<Exception, Object>。
我正在做一些测试，但是无法轻松测试我的方法的返回。
例如：
final Either<ServerException, TokenModel> result = await repository.getToken(...);
为了测试我能够做到这一点
expect(result, equals(Right(tokenModelExpected))); // => OK
现在如何直接检索结果？
final TokenModel modelRetrieved = Left(result); ==> Not working..
我发现我必须像这样进行投射：
final TokenModel modelRetrieved = (result as Left).value; ==> But I have some linter complain, that telling me that I shouldn't do as to cast on object...
我也想测试该异常，但是它不起作用，例如：
expect(result, equals(Left(ServerException()))); // => KO
所以我尝试了这个
expect(Left(ServerException()), equals(Left(ServerException()))); // => KO as well, because it says that the instances are different.
问题答案：
好的，这里是我的问题的解决方案：
提取/检索数据
final Either<ServerException, TokenModel> result = await repository.getToken(...);
result.fold(
(exception) => DoWhatYouWantWithException,
(tokenModel) => DoWhatYouWantWithModel
);
//Other way to 'extract' the data
if (result.isRight()) {
final TokenModel tokenModel = result.getOrElse(null);
}
测试异常
//You can extract it from below, or test it directly with the type
expect(() => result, throwsA(isInstanceOf<ServerException>()));
