📦 Lesson 4: Packages & Libraries

⏱ 25-35 min 📊 Intermediate 🏗️ Project-Based 🔥 Essential 2026 🔗 Official Source

🤔

Why Packages Matter

Imagine building a house where you have to craft every nail and brick yourself. Packages are like pre-built components - doors, windows, and fixtures you can just install!

❌ Without Packages

Copy-paste code everywhere
Hard to update
No version control
Reinventing the wheel

✅ With Packages

Import once, use everywhere
Easy updates via pub
Semantic versioning
40,000+ packages on pub.dev

🎯

Today's Project: "Super Utils" Package Suite

We'll create a professional package ecosystem:

📦 Core package with utility functions
🔧 CLI app that consumes the package
📚 Proper public API with exports
🧪 Test suite for the package
📋 Real pubspec.yaml configuration

Step 1

Understanding Package Structure

📁 Interactive Package Explorer

📁 super_utils/

📁 lib/

📄 super_utils.dart

📁 src/

🔒 string_utils.dart

🔒 math_utils.dart

🔒 date_utils.dart

📁 test/

📄 pubspec.yaml

📄 README.md

📄 File Details

Click on a file to see its purpose and contents!

🔑 Key Convention: lib/src/ is Private

Files in lib/src/ are conventionally private. Users of your package shouldn't import them directly. Instead, export them from the main library file.

import 'package:super_utils/super_utils.dart'; ✅ Correct - Uses public API

import 'package:super_utils/src/string_utils.dart'; ❌ Wrong - Bypasses public API

Step 2

Mastering pubspec.yaml

🏗️ Interactive pubspec.yaml Builder

Package Name:

Version:

Description:

Dependencies (comma-separated):

Dev Dependencies:

📄 Generated pubspec.yaml

name: super_utils
version: 1.0.0
description: A super collection of utility functions

environment:
  sdk: ^3.12.0

dependencies:
  http: ^1.3.0
  intl: ^0.19.0

dev_dependencies:
  test: ^1.24.0
  lints: ^5.0.0

Step 3

Designing Public API with Exports

🎨 API Design Playground

Choose which files to include in your public API:

src/string_utils.dart - String manipulation functions

src/math_utils.dart - Math helper functions

src/date_utils.dart - Date formatting utilities

src/internal_helpers.dart - Internal implementation details

📄 Generated lib/super_utils.dart

library;

export 'src/string_utils.dart';
export 'src/math_utils.dart';

💡 Best Practice: Only export files that form your public API. Keep internal helpers private so you can change them without breaking users.

Step 4

Managing Dependencies

🔗 Dependency Graph Visualizer

Your App

Click buttons to add dependencies and see the graph grow!

Step 5

Dart Workspaces (Modern 2026)

🏢 Multi-Package Workspace

📁 monorepo/

📄 pubspec.yaml (workspace root)

📁 super_utils/

📁 cli_app/

📁 web_service/

Root pubspec.yaml

name: _
publish_to: none

environment:
  sdk: ^3.12.0

workspace:
  - super_utils
  - cli_app
  - web_service

✨ Benefits:

Single pub get for all packages
Shared dependency resolution
Consistent versioning
Easier refactoring across packages

🏆

Build: Super Utils Package Suite

📝 String Utilities

🧪 Test Your Functions

🔢 Math Utilities

🧪 Test Your Functions

📅 Date Utilities

🧪 Test Your Functions

🌐 Explore pub.dev

📦 http

A composable, multi-platform, Future-based API for HTTP requests.

⭐ 1000+ likes | 🔄 Updated weekly

📦 intl

Internationalization and localization facilities.

⭐ 900+ likes | 🔄 Updated weekly

📦 path

A string-based path manipulation library.

⭐ 800+ likes | 🔄 Updated weekly

🎮 Package Master Quiz

🏆 Score: 0/6

⚡ Streak: 0

⏱ Time: 0s

🔓 Level: 1

Loading question...

🏅 Perfect Score ⚡ Speed Demon 🔥 Unstoppable