Incredibly shallow post. The level of validation and defensiveness in any piece of code will generally have to do with how close to the edge of your application it is — that is, how close to the input.

Functions near the core can assume more and code less defensively than those near the edge.

Libraries shouldnt be edge case first? What? /What kind/ of libraries? You really can’t imagine a library where it makes sense to code very defensively?

Also the post doesn’t even use “edge case” correctly. Definitionally you can’t have an edge case before you’ve defined the acceptable input. In their clamp function the edge case would be something like a large number on the border of graduating from long to BigInt or something. Edge case does not mean invalid input. Edge case is a rare/extreme input that is valid.