Packaging code for apps

To understand the importance of where you place your code, consider daily operations within a development team (even a small team). When you begin work on a ticket, you need to locate the code that you'll extend or alter. When your team member requests your review on a PR, you'll need to figure out how all the code changes in that PR relate to one another. When you and your team members start work every day, you're altering a shared codebase, which means you might make conflicting changes to the code that require extra effort to resolve.

For all of these reasons, you should package your app code in a way that keeps related code close together, and unrelated code further apart. Developers starting a new ticket will quickly find the relevant code. PR reviewers will easily recognize the relationship between changed files. And the team will operate with few, if any, merge conflicts.

A bundle of features and infrastructure

At a high level, an app is a bundle of features, which are backed by some amount of infrastructure that's shared across features. Breakdown your app package into those two groups.

/lib
  /infrastructure
  /features

Features

A feature is a customer-centric behavior within the app. Each feature deserves a directory and at least one file within your /lib/features directory. A photo-based social media app might breakdown features in the following manner.

/lib
  /features
    /feed
    /home
    /messaging
    /posting
    /profile
    /search
    /sign-in
    /sign-up

When multiple features are closely related, those features can be further bundled together.

/lib
  /features
    /feed
      /algorithmic
      /search
    /home
    /messaging
    /posting
    /user
      /profile
      /sign-in
      /sign-up

Infrastructure

Infrastructure refers to code that serves two or more features. Infrastructure code is bundled separately from features because it doesn't map one-to-one with any particular feature. You don't want code within the /posting feature used by the /messaging feature - that would prevent the development gains that we seek with code packaging.

The type of code that qualifies as infrastructure can vary greatly. It includes highly technical things like networking and database access. But it might also include business-centric things like subscription entitlements, as well as design-oriented concerns such as theming.

A photo-based social media app might breakdown infrastructure in the following manner.

/lib
  /infrastructure
    /authentication
      /gram_authentication.dart
      /google_authentication.dart
      /apple_authentication.dart
    /databases
      /realm.dart
    /photo_filters
    /networking
      /network_client.dart
    /ui_toolkit
      /buttons.dart
      /cards.dart
      /forms.dart
      /theme.dart

The Goal

The goal of this breakdown of code is to help developers quickly find relevant code, make changes to a small number of nearby files, and to review each others' changes quickly and with confidence.