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I think the issue is with checked exceptions as a solution to how to declare this signature, or at least with how they are designed in Java: if you add a new ex

I think the issue is with checked exceptions as a solution to how to declare this signature, or at least with how they are designed in Java: if you add a new exception to the signature, every downstream call site needs to change, recursively. This means it is impossible to add new exceptions to library methods without breakage, and even in your own code it may mean hundreds of changes throughout your code to add a new exception type. Rusts solution seems to have improved this conundrum, where you can describe how to map the new error into an existing hierarchy in a single or a few places instead of at every call site

kaba0 3y ago
> This means it is impossible to add new exceptions to library methods without breakage That’s a feature, not a bug. If it wouldn’t, an exception of that kind could bubble up at a place you didn’t expect. Also, it doesn’t require that many changes, it only has to be changed up to the point where you intend handling it. I don’t see how rust would be immune to that. Though it is true that polymorphism with respect to checked exceptions would be great. The new generation of languages might have that (e.g. Koka)
- wvenable 3y ago
  > If it wouldn’t, an exception of that kind could bubble up at a place you didn’t expect. You should always be able to handle an unknown exception. Sure you can't do much about it, but it shouldn't be a big deal. An exception only occurs if the code can't continue as expected. Libraries are supposed to be a point of abstraction. They should be allowed to change their implementation fundamentally as long as they continue to respect the same interface. Exceptions should not be part of the interface explicitly because are they implementation-detail related.
- nradov 3y ago
  If you don't control the code where the superclass or interface is defined then you're stuck. You can't change that code even if it would be only a tiny edit. Checked exceptions are absolutely not a "feature".

kaba0 3y ago

> This means it is impossible to add new exceptions to library methods without breakage That’s a feature, not a bug. If it wouldn’t, an exception of that kind could bubble up at a place you didn’t expect. Also, it doesn’t require that many changes, it only has to be changed up to the point where you intend handling it. I don’t see how rust would be immune to that. Though it is true that polymorphism with respect to checked exceptions would be great. The new generation of languages might have that (e.g. Koka)

wvenable 3y ago
> If it wouldn’t, an exception of that kind could bubble up at a place you didn’t expect. You should always be able to handle an unknown exception. Sure you can't do much about it, but it shouldn't be a big deal. An exception only occurs if the code can't continue as expected. Libraries are supposed to be a point of abstraction. They should be allowed to change their implementation fundamentally as long as they continue to respect the same interface. Exceptions should not be part of the interface explicitly because are they implementation-detail related.
nradov 3y ago
If you don't control the code where the superclass or interface is defined then you're stuck. You can't change that code even if it would be only a tiny edit. Checked exceptions are absolutely not a "feature".