Conventional error handling in programming typically involves using exceptions or returning error codes. While these approaches can work in some cases, they have several drawbacks that make them less than ideal in many situations:

1. Obscured control flow: When using exceptions, the control flow of your code can become obscured, making it harder to reason about. Exceptions can be thrown from anywhere in your code, making it difficult to know where errors might occur.
2. Null checks and boilerplate code: When returning error codes, you often need to write boilerplate code to check for errors and handle them appropriately. This can make your code more verbose and harder to read.
3. Difficulty in composition: Both exceptions and error codes can be difficult to compose, meaning that it can be hard to build more complex computations out of simpler building blocks. This can make it harder to write modular, reusable code.
4. Less expressive: Conventional error handling approaches can be less expressive than using a more functional approach like Either. For example, error codes typically only convey one piece of information (the error code), while an Either value can convey both the error message and a valid value.

By using Either or similar functional programming constructs, you can avoid many of these drawbacks and write more robust, expressive, and composable code. Functional programming is designed to help with managing the complexity of software development, including error handling.

The Either data type is useful when you have a computation that can result in one of two possible outcomes, such as success or failure, or a valid value or an error message. By representing these outcomes as Left or Right values inside an Either object, you can ensure that the result of your computation is always well-defined and easy to reason about.

Here are some benefits of using Either:

1. Explicit handling of errors: By using Either, you can explicitly handle errors and propagate them through your code. Since the error value is represented as a Left value, you can use the fold method to easily handle error cases.
2. Avoiding nulls: In many cases, Either can be used as a replacement for nullable types. Instead of returning null when a computation fails, you can return a Left value with an error message. This helps avoid null reference errors and makes your code more robust.
3. Clearer intent: By using Either, you make it clear to other developers what the possible outcomes of a computation are. This can make your code more readable and easier to reason about.
4. Composable: The Either type is composable, meaning you can use it with other functional programming constructs like map and flatMap. This allows you to build complex computations out of simpler building blocks.

Overall, using Either can help you write more robust, readable, and maintainable code.

The Either data type in the dartz package is a way to represent values that can be one of two possible types: either Left or Right. In Flutter, you can use Either to handle errors or other situations where there may be multiple possible outcomes.

To install the dartz package in a Flutter app, you can follow these steps:

1. Open your project’s pubspec.yaml file.
2. Add dartz as a dependency under the dependencies section:
   
   dependencies:
dartz: ^0.10.0
   
   Note that the ^ character before the version number means that you will get any patch or minor updates to version 0.10.0, but not major updates to a higher version.
3. Save the pubspec.yaml file.
4. In Android Studio or VS Code, run the following command in the terminal:csharpCopy codeflutter pub get This command will download and install the dartz package, as well as any other packages you have listed as dependencies in your pubspec.yaml file.
5. Once the package has been installed, you can import it in your Dart code like this:
   
   import 'package:dartz/dartz.dart';
   
   You can now use the Either and other types provided by the dartz package in your code.

That’s it! You’ve successfully installed the dartz package in your Flutter app.

Here’s an example of how to use Either in Flutter:

import 'package:dartz/dartz.dart';

Either<String, int> divide(int a, int b) {
  if (b == 0) {
    return Left('Cannot divide by zero');
  } else {
    return Right(a ~/ b);
  }
}

void main() {
  var result = divide(10, 2);
  result.fold(
    (error) => print('Error: $error'),
    (value) => print('Result: $value'),
  );  // Output: Result: 5
  
  var errorResult = divide(10, 0);
  errorResult.fold(
    (error) => print('Error: $error'),
    (value) => print('Result: $value'),
  );  // Output: Error: Cannot divide by zero
}

In this example, the divide function returns an Either<String, int> object, where the Left value is a String representing an error message and the Right value is an int representing the result of the division.

The fold method is used to extract the values from the Either object. If the result is a Right value, the fold method executes the first callback function, which prints the result. If the result is a Left value, the second callback function is executed, which prints the error message.

You can also use the map and flatMap methods on Either to transform the values inside it, just like you would with List or Stream.