Some notes on Dart package encapsulation

This is a short note showing how I use dart package encapsulation to manage the dependency in a dart/flutter application.

If you are new to creating your own dart package there is a great post here on dev to help u get started How to Create Dart Packages in Flutter: A Step-by-Step Guide

Dependencies are always an issue and need to be managed carefully to avoid cycles among other things, Golang helps by throwing a compilation error if u have any Cyclic dependencies in your code. Creating acyclic dependency trees(graphs) preferably Directed DAG is what you want, you can research the details if u r interested.

Say you have a project with a few packages like below

Here I have a rest_client package among others, the rest_client package will use other dependency packages like Dio.

I want to use Dio response types in the main code.

To keep the dependency tree clean I dont want to import Dio types in the main source as well as the rest_client package, so I export Dio from the rest_client package as so

library rest_client;

export 'package:dio/dio.dart';

In the main source code I import any needed Dio artifact from my rest_client package like

import 'package:rest_client/rest_client.dart' as transport;
class FreeAuthService  {

  final transport.Dio _dio = transport.Dio();
}

now I am free to encapsulate all my related http transport code in the rest_client package and just return the Dio responses into the main source code.

Here are some minor details

• packages are imported in pubspec like

  rest_client:
    path: packages/rest_client

• in the package directory source you need a top level file where you export the package dependencies you wish to expose like

library rest_client;

export 'package:dio/dio.dart';