Introducing Dartz: A Functional Programming Library for Dart/Flutter

Functional programming has been gaining popularity in recent years because of its numerous benefits such as improved readability, reusability, and maintainability of code. However, writing functional code can be challenging, especially for beginners. Fortunately, there are libraries that can help you implement functional programming concepts in your codebase with ease. One such library for Dart and Flutter is the Dartz package.

In this article, we’ll cover the basics of the Dartz package and how it can help you write better, more functional code in your Flutter applications.

What is Dartz?

Dartz is a functional programming library for Dart that provides abstractions and tools to help you write functional code. It includes features such as Option, Either, and Validated for handling null values, error scenarios, and data validation, respectively.

Dartz also provides utility functions such as map, filter, reduce, and fold for working with collections. These functions are similar to their counterparts in other programming languages and make it easier to manipulate collections in a functional style.

Installing Dartz

To use Dartz in your Flutter project, you need to add it as a dependency in your pubspec.yaml file. You can do this by adding the following line to the dependencies section of your pubspec.yaml file:

dependencies:
  dartz: latest

Option

The Option type is one of the most important data types provided by Dartz. It represents a value that may or may not exist. This type is useful for handling null values and reducing the need for null checks in your code.

There are two subtypes of the Option type: Some and None. The Some subtype represents a value that exists, while the None subtype represents a value that does not exist.

Here’s an example of how to use the Option type in Flutter

import 'package:dartz/dartz.dart';

void main() {
  final someValue = Some(42);
  final noneValue = None();

  someValue.fold(
    () => print('Value does not exist'),
    (value) => print('Value is $value'),
  ); // Output: Value is 42

  noneValue.fold(
    () => print('Value does not exist'),
    (value) => print('Value is $value'),
  ); // Output: Value does not exist
}

In the example above, we create instances of the Some and None subtypes and use the fold method to handle the possible presence or absence of a value.

Either

The Either type is another important data type provided by Dartz. It represents a value that can either be a success or a failure. This type is useful for handling error scenarios and propagating errors up the call stack.

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

import 'package:dartz/dartz.dart';

Either<String, int> divide(int a, int b) {
  if (b == 0) {
    return Left('Division by zero error');
  } else {
    return Right(a ~/ b);
  }
}

void main() {
  final result1 = divide(10, 2); // Returns Right(5)
  final result2 = divide(10, 0); // Returns Left(Division by zero error)

  result1.fold(
    (error) => print('Error: $error'),
    (value) => print('Result: $value'),
  ); // Output: Result: 5

  result2.fold(
    (error) => print('Error: $error'),
    (value) => print('Result: $value'),
  ); // Output: Error: Division by zero error
}

In the example above, we define a divide function that takes two integers as input and returns an Either type that can represent either a success (a non-zero result of division) or a failure (a division by zero error). If the denominator b is zero, we return a Left value containing an error message. Otherwise, we return a Right value containing the result of division.

In the main function, we call the divide function twice, once with b equal to 2 (a valid input) and once with b equal to 0 (an invalid input). We then use the fold method on the Either values to handle both the success and failure cases. In the success case, we print the result of division. In the failure case, we print the error message.

You can find the GitHub repo for this project here:

https://github.com/faheem-riaz/functional_programming_dartz

LinkedIn: https://www.linkedin.com/in/faheemriaz/