Ep 097: Application of Composition► Play Episode
Each week, we discuss a different topic about Clojure and functional programming.
This week, the topic is: "composing your application". We get a handle on bringing I/O resources together in an application.
Our discussion includes:
- What is a "handle"? Why is it called that?
- More puns!
- How do you handle I/O handles?
- How do you keep the pure and side-effecting parts away from each other?
- Managing and organizing application components.
- What is a framework vs a library?
- "Injection style" vs "singleton style".
- How far down the call stack should handles travel?
- Figuring out a start-up order and a shut-down order.
- How obtaining a resource can negatively affect composition.
- Separating the knowledge of finding a resource vs using a resource.
- The concept of an "application index".
- Why all this matters for long-term maintenance.
- Using feature flags.
- The two developers on every software project.
- What is the "band-aid test"?
- "If a program does a bunch of computation, but it doesn't have any I/O, did it do anything?"
- "Handles inherently are going to hurt you. You don't even have a hold on the whole thing. You have a little bit that you can use to to access that external system."
- "I visualized an axe or a knife. You have a handle, but you have to watch out for what the handle is connected to!"
- "In Clojure, I think of frameworks as an integration between your code and the purpose of that framework as opposed to the foundational layer that glues your whole world together."
- "Even in OO, it's a smell if I/O handles travel too far and wide!"
- "Lots of assuming!"
- "Sometimes ad hoc is confused with flexibility. You didn't have to think about it, so it felt flexible, but it just happened."
- "Composition is about being able to use things in multiple ways."
- "If you are accessing a singleton state from a function, you are no longer side effect free."
- "Why would I ever save anything anywhere other than the place the application has configured as its database?"
- "Have you ever had a physical "dead tree" book?"
- "Where are all the components?"
- "With the index style, you have a clear delineation of all the parts of the software and how they're connected together."
- "Whenever you start using a library or framework, you are hopefully solving a problem, but you're also inviting complexity in. You have to be wary of what it allows you to do, and what it allows future developers to do."
- "If you pull that band-aid off, how many little hairs are going to come off with it? How badly is it going to hurt?"
- "One of the tests of composability is the surface area of contact. More is not better!"