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Unchecked exceptions are a disaster. In C# when you call a method you have no idea what exceptions can be thrown by the called method unless you inspect the cal

Unchecked exceptions are a disaster. In C# when you call a method you have no idea what exceptions can be thrown by the called method unless you inspect the called method and all the methods called by it. The called method can be modified at any time and a new exception can be thrown and your code will compile just fine. This is bad because the new exception may be a recoverable condition and instead of recovering your program will crash. This is why exceptions that can be thrown by a method should be considered part of the signature of the method and you should get a compile-time error (as opposed to a runtime crash) if the method throws a new exception that wasn't there when you originally wrote the code.

mrec 7y ago
> In C# when you call a method you have no idea what exceptions can be thrown Well, you have no idea in Java either, given that unchecked exceptions exist. I understand the goal of checked exceptions, I just haven't found much value in them in practice, and given that nobody has copied them I don't think I'm alone. I'm sure it depends what area you're working in, but in my experience it's rare (not unknown, but rare) to be able to do much with e.g. an `IOException` at the call site, and naive approaches like automatic retry can easily be worse than crashing if those retries end up looping excessively and spamming a resource that was already struggling. My personal preference is for non-exception mechanisms (Maybe/Option/Result objects, or C#'s TryXXX methods) to handle recoverable cases, and unchecked exceptions with very high-level catchers to convert the nonrecoverable ones into sensible diagnostics. YMMV, obviously.
jcranmer 7y ago
As my opinions on exceptions have evolved throughout the years, I've come to think that there is value to unchecked exceptions, but unchecked exceptions need a fundamentally different mode from checked exceptions. The best motivation for unchecked exceptions are things like division by 0, or null pointer dereferences: these are things that result from programmers misusing the API, and are generally unrecoverable. What you want instead is some sort of "graceful crash"--for example, if you're a web server, display a 500 page and log the stack trace somewhere internally. Using a pretty distinct mechanism for driving these error cases (e.g., Rust's panic mechanism) I think works better for emphasizing the crash aspect here. Of course, now you have the regular checked exceptions which are a fundamental part of the function type. It's not clear to me that the try/catch/throw model is necessarily the best model for propagating these exceptions, and there are several cases where the overhead involved in the (misleadingly named) zero-cost exception handling model are not appropriate for the model. Although there is something to be said for easy upgrading of checked into unchecked exceptions. It's a relatively natural assertion that something can't fail for reasons the compiler doesn't understand (which means informing the programmer when and where it failed is very critical!). I've always been annoyed by Eclipse deciding that the default implementation of catch should be "ignore the exception" instead of "wrap it in a RuntimeException."

mrec 7y ago

> In C# when you call a method you have no idea what exceptions can be thrown Well, you have no idea in Java either, given that unchecked exceptions exist. I understand the goal of checked exceptions, I just haven't found much value in them in practice, and given that nobody has copied them I don't think I'm alone. I'm sure it depends what area you're working in, but in my experience it's rare (not unknown, but rare) to be able to do much with e.g. an `IOException` at the call site, and naive approaches like automatic retry can easily be worse than crashing if those retries end up looping excessively and spamming a resource that was already struggling. My personal preference is for non-exception mechanisms (Maybe/Option/Result objects, or C#'s TryXXX methods) to handle recoverable cases, and unchecked exceptions with very high-level catchers to convert the nonrecoverable ones into sensible diagnostics. YMMV, obviously.

jcranmer 7y ago

As my opinions on exceptions have evolved throughout the years, I've come to think that there is value to unchecked exceptions, but unchecked exceptions need a fundamentally different mode from checked exceptions. The best motivation for unchecked exceptions are things like division by 0, or null pointer dereferences: these are things that result from programmers misusing the API, and are generally unrecoverable. What you want instead is some sort of "graceful crash"--for example, if you're a web server, display a 500 page and log the stack trace somewhere internally. Using a pretty distinct mechanism for driving these error cases (e.g., Rust's panic mechanism) I think works better for emphasizing the crash aspect here. Of course, now you have the regular checked exceptions which are a fundamental part of the function type. It's not clear to me that the try/catch/throw model is necessarily the best model for propagating these exceptions, and there are several cases where the overhead involved in the (misleadingly named) zero-cost exception handling model are not appropriate for the model. Although there is something to be said for easy upgrading of checked into unchecked exceptions. It's a relatively natural assertion that something can't fail for reasons the compiler doesn't understand (which means informing the programmer when and where it failed is very critical!). I've always been annoyed by Eclipse deciding that the default implementation of catch should be "ignore the exception" instead of "wrap it in a RuntimeException."