Comment by miki123211

I view types as "the thing that prevents programmers and agents alike from writing bad and incorrect code in the future". They're a way of encoding invariants that doesn't require the programmer to worry about accidentally breaking them (because breaking the invariant will cause a compiler error).

Types are not the only way to encode such invariants. tests (and to a smaller extend lints and agent hooks) are other such mechanisms.

On this beat, I think people really under-appreciate the value of tests that check the structure of code to verify some general property, instead of checking the behavior of particular code paths.

At work, we have an internal system where we use a specific type to pass certain information around. It is extremely easy to construct an (empty) instance of that type wherever it is needed, but that is almost always wrong, you actually have to do the work and figure out how to get a real instance from somewhere. To make matters worse, whether the instance is empty or not doesn't matter in development, but matters a lot in production.

Because agents are lazy, they tend to construct empty instances whenever they feel like it, and there was no immediate feedback mechanism that could tell them it was wrong. It's not something you can easily encode in a type for example. I therefore build one (imperfectly, based on ruff lints), but it solved the problem entirely.