That's a valid point but it's somewhere on a spectrum of "quick to write/change" vs "safe and validated" debate of strictly vs loosely typed systems. Strictly typed systems are almost by definition much more "brittle" when it comes to code editing. But the strictness also ensures that refactoring is usually less perilous than in loosely typed code.

And as with async, the issue is a) the lack of the ability to write generic code that can abstract over the async-ness or throw signature of a function and b) the ability to type erase asyncness (by wrapping with stackful coroutines) or throw signature (by converting to unchecked exceptions).

Incidentally, for exceptions, Java had (b), but for a long time didn't have (a) (although I think this changed?), leading to (b) being abused.

Unhappy way is a part of contract. So yes, that is what I want. If a function couldn't fail before but can after the update - I want to know about it.

In fact, at each layer, if you want to propagate an error, you have to convert it to one specific to that layer.

> Checked exceptions, in contrast to unchecked, means that if a function/method deep in your call stack is changed to throw an exception, you may have to change many function (to at least denote that they will throw that exception or some exception) between the handler and the thrower.

That's the point! The whole reason for checked exceptions is to gain the benefit of knowing if a function starts throwing an exception that it didn't before, so you can decide how to handle it. It's a good thing, not a bad thing! It's no different from having a type system which can tell you if the arguments to a function change, or if its return type does.

Why are you screaming? All those wasted exclamation marks, you could have written something I didn't know. I didn't say it wasn't the point or that it was a bad thing.

> Setting aside the objections some have to exceptions generally: Checked exceptions, in contrast to unchecked, means that if a function/method deep in your call stack is changed to throw an exception, you may have to change many function (to at least denote that they will throw that exception or some exception) between the handler and the thrower. It's an objection to the ergonomics around modifying systems.

And if you change a function deep in the call stack to return a different type on the happy path? Same thing. Yet, people don't complain about that and give up on statically type checking return values.

I honestly think the main reason that some people will simultaneously enjoy using Result/Try/Either types in languages like Rust while also maligning checked exceptions is because of the mental model and semantics around the terminology. I.e., "checked exception" and "unchecked exception" are both "exceptions", so our brains lumped those two concepts together; whereas returning a union type that has a success variant and a failure variant means that our brains are more willing lump the failure return and the successful return together.

To be fair, I do think it's a genuine design flaw to have checked and unchecked exceptions both named and syntactically handled similarly. The return type approach is a better semantic model for modelling expected business logic "failure" modes.