Monorepo: The Key to Streamlined Development in Modular Applications

In modern software development, as applications grow larger and more complex, managing separate codebases for different modules can become a significant challenge. This was the case in our application, where we initially followed a multi-repo structure with separate repositories for each module.

Challenges with Multi-Repo Structure:

The main issue we faced with this structure was the high potential for conflicts when multiple developers worked on the same application. Specific problems included:

• Branching Conflicts: One developer working on a branch for a particular module could make changes that impacted other modules. As each module had its own repo, we had to deal with conflicts across various repositories.

• High Maintenance: Each module had to be maintained separately, with separate branches for every feature or bug fix. This meant handling multiple branches across several repositories, which became a hassle.

• Cross-Module Dependencies: Changes in one module required syncing and coordination across other modules, creating delays and inefficiencies.

As our team grew, these issues became increasingly problematic, and the complexity of managing multiple repositories started to slow down the development process. We realized that the multi-repo approach was no longer sustainable for us.

The Transition to Monorepo

To address these issues, we decided to transition to a monorepo structure. A monorepo consolidates all modules and services into a single repository, making it easier to manage and coordinate changes across the entire application.

In our case, we structured the monorepo using Swift Package Manager (SPM) modules, which allowed us to encapsulate each feature or module into its own isolated Swift package within the same repository.

Benefits of Monorepo Structure:

1. Simplified Dependency Management: With a monorepo, we no longer needed to maintain separate repositories or worry about cross-repo dependencies. All modules exist within a single repository, so changes in one module are immediately reflected across the application.

2. Better Collaboration: Multiple developers can now work on the same repository without the risk of conflicts due to scattered modules in separate repos. This centralization makes it easier for team members to coordinate their work.

3. Faster Integration: Changes across different modules are integrated more quickly, as developers no longer need to pull updates from multiple repositories. The SPM modules ensure that dependencies are well-isolated but still accessible in the same repository.

4. Easier Version Control: All the code is versioned together, making it easier to track changes and rollback if needed. There’s no need to synchronize branches or versions across multiple repositories.

Challenges with Monorepo

While the monorepo has solved many of our previous issues, it also introduced a few limitations:

• Encapsulation for Debugging: In the monorepo, modules are encapsulated within their own SPM packages, which makes navigation and debugging slightly more challenging. Unlike a traditional monolithic structure, where all the code is easily accessible, encapsulation requires developers to navigate through the layers. You can no longer just search for a class or structure—you have to locate the reference and follow it with Cmd + Click to navigate to the relevant module.

• Encapsulation vs. Visibility: Since the code is more encapsulated, understanding how different modules interact becomes more difficult compared to when everything was in a monolithic structure. Debugging often requires more steps to trace the relationships between modules.

Code Example: How We Structured Our Monorepo Using SPM Modules

import PackageDescription

let package = Package(
    name: "OurApplication",
    platforms: [
        .iOS(.v14)
    ],
    products: [
        // The app product that combines all modules
        .library(name: "OurApp", targets: ["CoreModule", "NetworkModule", "UIModule"])
    ],
    dependencies: [
        // Add third-party dependencies here
    ],
    targets: [
        // Core Business Logic Module
        .target(name: "CoreModule", dependencies: []),
        
        // Network Layer Module
        .target(name: "NetworkModule", dependencies: ["CoreModule"]),
        
        // UI Layer Module
        .target(name: "UIModule", dependencies: ["CoreModule", "NetworkModule"]),
    ]
)        

Each module (e.g., CoreModule, NetworkModule, UIModule) is encapsulated as an SPM package, but all exist within the same monorepo. This allows for modularity without the overhead of multiple repositories.

Conclusion:

The transition from multi-repo to monorepo has simplified our development process by centralizing our modules and reducing branching conflicts. While there are still challenges with encapsulation and debugging, these are outweighed by the advantages of a monorepo structure.

We encourage teams facing similar challenges to consider a monorepo approach, especially if multiple resources are working on the same application.

We would love to hear your suggestions on improving this aspect. How do you manage efficient debugging and searching for classes or structs in a monorepo structure, especially when using Swift Package Manager or similar setups?

Any tools, tips, or practices that you’ve found helpful would be greatly appreciated!

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