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Hi, welcome to RubyKaigi Takeout 2020.
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I hope you're enjoying all the content.
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Today, I will be reflecting on Ruby reflection for rendering RBIs.
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My name is Ufuk Kayserilioglu, and I'm a Production Engineering Manager on the Ruby Infrastructure Team at Shopify.
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A quick introduction to the concept: When I joined Shopify at the beginning of 2019, the first project I worked on was the adoption of Sorbet on our codebase.
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For those of you who don't know, Sorbet is a static type checker built by the fine people at Stripe.
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In the project I was involved with, we were trying to adopt gradual typing using Sorbet on our Rails monolith.
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As we were working on this adoption, we quickly realized that we had a problem with RubyGems.
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The issue was that Sorbet doesn't look into your gem dependencies, meaning it has no way of knowing what has been exported from those gems.
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It only type checks your user code, which is problematic because the cost of entry for gradual typing adoption with Sorbet is for all references to constants in your code to be resolved.
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If you refer to a constant or a module in your code, Sorbet needs to know what that constant is, but unfortunately, because it doesn't know the constants coming from gems, it has no visibility into them.
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Let me provide a quick example to illustrate this.
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For instance, if you have a MyCLI class that subclasses from Thor and calls the class option method, when you try to type check this with Sorbet, Sorbet will be confused because it won't recognize Thor or the class option method.
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Without knowing the specifics of the class and its parameters, Sorbet can't successfully type check it because it cannot verify if 'assemble' is the correct type.
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The way to solve this issue, developed by the Stripe team, was the concept of Ruby Interface files, or RBIs.
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Ruby interface files are essentially Ruby files that declare classes and methods without all the implementation details.
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This means that if you provide Sorbet with an RBI file that specifies what classes and methods exist, Sorbet can successfully type check user code that references those symbols.
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However, creating and maintaining these RBI files manually for the over 400 gems we depend on at Shopify is a nightmare.
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We needed a way to automate the generation of these files using Ruby’s reflection capabilities, which allows us to dynamically inspect and manipulate the structure of our Ruby classes and modules.
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Reflection is the ability of a program to examine or manipulate the type properties, methods, or values of an object at runtime.
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We often use reflection in Ruby, often unknowingly, as every time you call define_method or alias_method, you are engaging in reflection.
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For our purpose, we focused on the introspection aspect, which allows us to read information about classes and methods without modifying them.
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Before we start, it's important to understand that, in Ruby, everything is treated as a constant.
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When declaring a class or module, you're actually creating a constant, and there’s a notable relationship between classes and constants.
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For example, defining a class does not just create a class; it creates a constant that refers to that class.
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This is critical because we will need to inspect these constants from our code to understand their relationships and generate the corresponding RBIs.
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We’ll take a look at the methods and constants in the Store class as an example.
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Using Ruby reflection, we can programmatically obtain the information required to construct our RBIs.
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The key to this process is accessing constants by name, checking if they exist, and then retrieving references to them for further inspection.
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Once we have references to the relevant classes, we can query them for their methods, superclass, constants, and included modules.
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By retrieving this data, we can generate the corresponding structure for our RBIs, which is essential for enabling Sorbet to type-check the gem code our application depends on.
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Each section of this process relies on Ruby's reflection mechanisms to access all necessary code elements dynamically.
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One common obstacle we face in runtime reflection is dealing with dynamic code, where constants or methods may change during runtime.
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We must ensure that our reflection code can handle such cases gracefully to avoid errors in our automated RBI generation.
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As we continue, I will discuss the key aspects of using Ruby reflection effectively, while also addressing potential pitfalls that developers should be aware of.
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One such pitfall is the misuse of constants, where classes redefine their own identity or functionality in ways that complicate our ability to introspect.
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We must be vigilant against those who may try to create convoluted hierarchies or override critical methods like 'name' and 'superclass' without adhering to the expected norms.
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Contending with these discrepancies can lead to errors in type-checking and hinder our development progress, as Sorbet will fail to correctly understand the constant’s behavior.
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Another consideration is handling private constants, especially with classes where the superclass is private.
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In this case, Sorbet may not properly assess the class hierarchy, leading to confusion and errors that could easily have been avoided.
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We utilize reflection to check and bypass these methods when necessary, ensuring a smoother experience when generating RBIs.
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Now, let's delve into how we can dynamically create and utilize a comprehensive set of RBIs for various gems, employing both manual insights and automated processes.
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This interaction opens the door for a streamlined integration of third-party gems into our projects, allowing for effective use of type-checking throughout our codebase.
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When working with dynamic languages such as Ruby, it's crucial to rely on both introspection and reflection to maintain flexibility and resilience against potential issues.
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In summary, we can successfully generate Ruby Interface Files while mitigating the complexities introduced by Ruby's dynamic nature, thereby leading to a more robust development experience.
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It's an evolving learning process that fosters strong collaboration and innovative resolution of challenges faced on a day-to-day basis.
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To conclude, I encourage you to explore the options available for enhancing your development processes using Sorbet, and oversee your Ruby code with clarity and confidence.
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If you're interested in leveraging the capabilities discussed today, I invite you to check out the tapioca gem which we have open-sourced for your convenience.
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You can access it through GitHub and, of course, feel free to engage with me for inquiries or feedback related to this topic.
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Thank you for your time. It was a pleasure speaking at RubyKaigi Takeout 2020. I hope to see you around!
