Lightning talk: Sliced Ruby - Enforcing module boundaries with private_const and packwerk

by Severin Ráz

In the lightning talk entitled "Sliced Ruby - Enforcing module boundaries with private_const and packwerk," Severin Ráz discusses effective strategies for modularizing applications in Ruby, particularly transitioning from chaotic codebases to more organized structures. The talk emphasizes the importance of maintaining clear module boundaries to prevent unintended coupling between classes and components.

Key points discussed include:

Significance of Modularization: Ráz highlights the common pitfall where developers end up with a 'big ball of mud' in their applications and emphasizes the importance of modularizing code to avoid this chaos.
Tools for Enforcing Boundaries: Two main tools are introduced for module management: private_constant, a built-in Ruby feature, and Packwerk, a gem designed to help enforce module boundaries and usage permissions.
Using private_constant: Ráz illustrates private_constant through an example featuring a Taxes module. He explains how making the TaxDetails class private prevents external classes from accessing it directly, thereby enforcing proper usage via the public Apply class. This redesign helps prevent tight coupling and eases maintenance.
Introduction to Packwerk: The talk transitions to Packwerk, which helps define and verify module interactions within the application. Ráz explains how Packwerk allows developers to specify which modules can communicate, enhancing the architecture's clarity and maintainability. It also supports a layered architecture approach, where rules about communication between layers can be effectively enforced.
Continuous Improvement with Packwerk: Ráz discusses how Packwerk can be integrated into continuous integration (CI) setups, providing ongoing verification of module violations through alerts and checklists. This allows teams to address issues incrementally, facilitating a smoother transition to better modular practices.
Additional Tools and Visualizers: The talk concludes with Ráz mentioning the additional functionalities Packwerk offers, including visualization tools to generate diagrams of module structures for better understanding.

In summary, the main takeaways from the talk are the importance of modularization in Ruby applications and the effective use of tools like private_constant and Packwerk to enforce module boundaries. Ráz encourages developers to embrace these tools to build robust and maintainable modularized monoliths, inviting attendees to engage further at their booth.

00:00:05.279 So, you want to build a majestic monolith. However, what you often end up with is a big ball of mud. Perhaps you have recently started a new job and inherited a big ball of mud. If you want to transition from this chaotic state to a more organized structure, one effective approach is to modularize your application.

00:00:14.480 There are various strategies and best practices regarding how to modularize your application. However, that won't be the focus of this talk. Instead, we will explore two tools that can help you effectively implement modules and ensure you do not unintentionally break your module boundaries. The important aspect of these tools is that they allow for incremental changes, enabling you to apply them step by step at your own pace, especially if you are working with an existing codebase.

00:00:38.719 The tools we will examine are `private_constant` and `Packwerk`. Let's start with `private_constant`. This is a built-in feature of Ruby and part of the language itself. To illustrate this, let’s consider an example. Imagine you have a module called `Taxes` consisting of two classes: `TaxDetails`, which contains logic for calculating taxes; and `Apply`, which acts as the service object.

00:01:09.759 Clients of your module are expected to use the `Apply` class if they want to calculate something. In the example provided, we successfully shipped this setup. However, later on, someone might write a view that directly uses the `TaxDetails` class, which is intended to be internal. This is not desired, as it couples the view to `TaxDetails`. If changes occur within the `Taxes` module, it may break the view, necessitating additional fixes.

00:01:32.799 To resolve this issue, we can return to our `Taxes` module and introduce the `private_constant` statement, thereby making the `TaxDetails` class private to the module. Now, if a programmer attempts to access it from the view, they would encounter an exception. This indicates they will need to revisit the `Taxes` module to comprehend the intended usage. The `private_constant` feature can be utilized right away, helping you define your module's API by clearly indicating which parts are public.

00:02:31.560 By having a well-defined API, you can also enhance your code documentation, ensuring that anyone who needs to use or understand the module can easily find the relevant information.

00:03:01.360 Now let's transition to Packwerk. Packwerk is a gem that allows you to define which parts of your module are meant to be used by others. Furthermore, you can specify who these others are. For example, you might dictate that your tax use case is permitted to interact with the `Tax` module, but disallow the support use case to prevent unwanted coupling.

00:03:10.560 Packwerk also enables you to structure your application into layers. You can specify that only upper layers are allowed to communicate with lower layers, or that outer layers may interact with inner layers. Once you've defined these rules, Packwerk can verify compliance. This verification can also occur within your continuous integration (CI) setup.

00:03:36.720 Packwerk, developed by Shopify, is well-maintained. It offers a to-do list feature similar to RuboCop, allowing you to define rules, analyze your code, and generate a checklist of items. Known rule violations will be ignored by the checker, allowing you to continue your work. Should you introduce new violations, your checker will alert you. Additionally, you can address issues at your own pace, enabling a gradual improvement process.

00:04:22.880 There is much more to discover with Packwerk, including tools like visualizers that can generate diagrams of your application's module structure. Today, we have reviewed two tools: `private_constant`, a Ruby built-in that can be implemented immediately, and Packwerk, which requires more setup but offers greater capabilities.

00:04:45.240 Here are my contact details. We have a booth in the back where you can join us for a chat and say hi. Have fun building modularized monoliths!