Functional Programming in Flutter using fpdart

As I build my budgeting app, functional programming has become a key part of my development. The fpdart package has really helped me manage errors and state in a more organized way. Let me show you how it’s made a difference with some practical examples.

Why Functional Programming?

Functional programming makes code easier to manage and test by focusing on pure functions and immutability (not changing data).

How Fpdart Helps

Fpdart offers tools like Either and Option that simplify error handling and dealing with nullable values. Instead of using lots of null checks, I use Either to handle success and failure in a cleaner way.

Here’s how I use Either in my budgeting app:

import 'package:fpdart/fpdart.dart';

// Get budget data
Future<Either<Failure, Budget>> getBudget(String userId) async {
    try {
        final budget = await api.fetchBudget(userId); // API call
        return Right(budget); // Success
    } catch (error) {
        return Left(Failure('Failed to fetch budget data')); // Failure
    }
}

Handling Errors with Either

Handling results in the UI:

void displayBudget(String userId) async {
    final result = await getBudget(userId);

    result.fold(
            (failure) => showError(failure.message), // Show error message
            (budget) => showBudget(budget), // Display budget
            );
        }

With Either, I can separate successful results (Right) from errors (Left), making my code easier to understand.

The fold method helps me deal with both success and failure in a clean way, keeping the code neat and the UI responsive.

Using Option for Nullable Values

Fpdart’s Option helps manage nullable values without constant null checks. This way, I can handle the presence or absence of values more smoothly.

Option<Budget> findBudgetById(List<Budget> budgets, String id) {
    final budget = budgets.firstWhereOrNull((b) => b.id == id);
    return Option.fromNullable(budget);
}

Instead of checking if budget is null, I can handle it like this:

final optionBudget = findBudgetById(budgets, '123');

optionBudget.match(
        () => print('Budget not found'), // Handle missing budget
        (budget) => print('Found budget: $budget'), // Handle found budget
    );

• fpdart (pub.dev)
• fpdart (Github)

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