Result Monad Example 2

result_monad_2.dart

///
/// The Result Monad
///
abstract class Result<T> {
  bool isSuccess() {
    return this is Success;
  }
  
  Success<T> asSuccess() {
    return this as Success<T>;
  }
  
  Failure asFailure() {
    return this as Failure;
  }
  
  Result bind(Result Function(Result) doNext) {
    if (isSuccess()) {
      return doNext(this);
    } else {
      return this;
    }
  }
}

class Success<T> extends Result {
  Success(this.result);
  
  T result;
}

class Failure extends Result {
  Failure(this.message);
  
  String message;
  
  
}

///
/// Our Models
///

class User {}
class RealEstate {}

///
/// The service
///
Result fetchUser() {
  return Success(User());
  //return Failure("Sorry, the network was pretty bad fetching user");
}

Result fetchRealEstate(int id) {
  //return Success(RealEstate());
  return Failure("Sorry, the network was pretty bad");
}


void main() {
  final result = fetchUser()
      .bind((userResult) => fetchRealEstate(1))
      .bind((userResult) => fetchRealEstate(2));
  
  if(result.isSuccess()) {
    print(result.asSuccess().result);
  } else {
    print(result.asFailure().message);
  }
}