This is the sort of thing that makes me love (or hate) a codebase. I just have to point out that this sort of thing is extremely easy to do with typed languages

This is the sort of thing that makes me love (or hate) a codebase. I just have to point out that this sort of thing is extremely easy to do with typed languages, and can be (but not inherently) a total nightmare with untyped languages. Types matter, not just for correctness, but also cleanliness, order, and ease of maintenance.