Mastering Flutter Architecture: From CLEAN to Feature-First for Faster, Scalable Development

Understanding CLEAN Architecture in Flutter and Alternatives

In the Flutter development community, CLEAN architecture has gained traction for its organized structure and separation of concerns. Proposed by Uncle Bob, this architecture aims to make code more maintainable by dividing it into layers such as data, domain, and presentation. However, while the approach is theoretically sound, it has its challenges in practice, especially for those looking for simplicity and scalability.

In this article, we will explore why CLEAN architecture, though popular, may not always be the best solution. We will also look at two alternatives: feature-first and mixed approaches, which can simplify project structures while maintaining clarity.

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What is the Problem with CLEAN Architecture?

The problem with CLEAN architecture often arises from its layer-first nature. In a typical CLEAN setup, files related to a particular feature (e.g., "Orders") are distributed across multiple folders. Let's consider the following folder structure:

Image 0: Traditional CLEAN Architecture

In this setup:

• app contains configurations, extensions, services, and other essential utilities.
• data has models, providers, and repositories.
• domain is used for entities and use cases.
• presentation holds controllers and UI-related files, spread across multiple subfolders.

For instance, the files related to the "Orders" feature might be scattered like this:

• order_model.dart in the data/models folder.
• order_service.dart in the data/providers folder.
• order_list_controller.dart and order_details_controller.dart in presentation/controllers.
• UI files like order_list_view.dart and order_details_view.dart in different subfolders under presentation/pages.

While this separation of concerns is great in theory, it leads to inconvenience in real-world projects. A developer working on a specific feature, such as "Orders," may need to switch between multiple folders, leading to fragmentation and slower development speed.

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Why is it Inconvenient?

The key issue with CLEAN architecture lies in its overly layered structure, which increases complexity. For beginners, this can be intimidating, and for experienced developers, it can be inefficient when iterating on features.

As shown in Image 0, the CLEAN architecture leads to a structure where related files are separated by their roles in the system (models, services, controllers, etc.), but not by the feature they belong to. This complicates navigating and maintaining the codebase.

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Simpler Alternatives: Feature-First Architecture

To address these problems, the feature-first architecture is a simpler, more scalable solution. Instead of organizing code by layer (data, domain, presentation), it organizes it by feature. This way, all the files related to a particular feature like "Orders" are in one place.

Image 1: Feature-First Structure

In Image 1, the folder structure is organized by feature:

• auth/ contains everything related to authentication.
• orders/ contains the order_model.dart, order_service.dart, order_details_controller.dart, order_list_controller.dart, and their corresponding views all in one place.

This structure is highly intuitive:

• Easy to maintain: Developers can find all relevant files for a feature in a single folder.
• Scalable: New features can be added by simply creating new folders, without affecting existing structures.

For example, the "Orders" feature has all the necessary files (controller, model, view) in one folder, making it much easier to work on than jumping between multiple directories.

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Mixed Approach: A Balanced Middle Ground

For developers who prefer some level of layer separation but want to keep things simpler than CLEAN, a mixed approach can be useful. In this approach, there are only two main layers: view and data. Within these layers, files are organized by feature, offering the benefits of both worlds.

Image 2: Mixed Approach

In Image 2, the project is divided into common, data, and view layers:

• common contains shared components, constants, and utilities.
• data has feature-related services and models. For example, order_model.dart and order_service.dart are in the data/order folder.
• view contains all UI components. For example, order_details_view.dart and order_list_view.dart are grouped in their respective subfolders like view/order_details and view/order_list.

This hybrid approach ensures that while data and view files are separated into their respective layers, they are still organized by feature within those layers. Developers can maintain separation of concerns without the overhead of deeply nested and fragmented file structures.

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Advanced Mixed Approach: Modular Organization

If you want to further modularize your application, another variation of the mixed approach can be used. In this, the modules folder groups feature-specific data and views.

Image 3: Modular Organization

In Image 3, the modules folder contains:

• order_details and order_list submodules, each with their own controller and view subfolders.
• This approach extends the feature-first philosophy by grouping all logic for individual screens or modules, keeping things clean and organized.

Here, each feature module is almost self-contained, allowing for better modularization and isolation, which can help with testing and reusability.

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Conclusion

While CLEAN architecture is well-known in the Flutter community, it is not always the best fit for every project. It tends to lead to overly complex and fragmented structures, making navigation and maintenance more challenging. A feature-first approach, as seen in Image 1, is much simpler, making it easy to scale as the project grows.

For those who prefer a little separation, the mixed approach shown in Images 2 and 3 offers a balance between simplicity and organization, separating data and views but still keeping features together.

Choosing the right architecture for your Flutter project depends on your team's needs and preferences, but it’s crucial to prioritize simplicity and scalability to ensure smooth development and maintainability over time.