It's the same blind spot people have to Java's checked exceptions. People commonly resort to Pokemon exception handling and either blindly ignoring or rethrowing as a runtime exception. When Rust got popular, I was a bit confused by people talking about how great Result it's essentially a checked exception without a stack trace.
"Checked Exceptions Are Actually Good" gang, rise up! :p
I think adoption would have played out very different if there had only been some more syntactic-sugar. For example, an easy syntax for saying: "In this method, any (checked) DeepException e that bubbles up should immediately be replaced by a new (checked) MylayerException(e) that contains the original one as a cause.
We might still get lazy programmers making systems where every damn thing goes into a generic MylayerException, but that mess would still be way easier to fix later than a hundred scattered RuntimeExceptions.
Exception handling would be better than what we're seeing here.
The problem is that any non-trivial software is composition, and encapsulation means most errors aren't recoverable.
We just need easy ways to propagate exceptions out to the appropriate reliability boundary, ie. the transaction/ request/ config loading, and fail it sensibly, with an easily diagnosable message and without crashing the whole process.
C# or unchecked Java exceptions are actually fairly close to ideal for this.
The correct paradigm is "prefer throw to catch" -- requiring devs to check every ret-val just created thousands of opportunities for mistakes to be made.
By contrast, a reliable C# or Java version might have just 3 catch clauses and handle errors arising below sensibly without any developer effort.
I'm with you! Checked exceptions are actually good and the hate for them is super short sighted. The exact same criticisms levied at checked exceptions apply to static typing in general, but people acknowledge the great value static types have for preventing errors at compile time. Checked exceptions have that same value, but are dunked on for some reason.
1. in most cases they don't want to handle `InterruptedException` or `IOException` and yet need to bubble them up. In that case the code is very verbose.
2. it makes lambdas and functions incompatible. So eg: if you're passing a function to forEach, you're forced to wrap it in runtime exception.
3. Due to (1) and (2), most people become lazy and do `throws Exception` which negates most advantages of having exceptions in the first place.
In line-of-business apps (where Java is used the most), an uncaught exception is not a big deal. It will bubble up and gets handled somewhere far up the stack (eg: the server logger) without disrupting other parts of the application. This reduces the utility of having every function throw InterruptedException / IOException when those hardly ever happen.
Java checked exceptions suffer from a lack of generic exception types ("throws T", where T can be e.g. "Exception", "Exception1|Exception2", or "never") This would also require union types and a bottom type.
Without generics, higher order functions are very hard to use.
In my experience, it actually is a big deal, leaving a wake of indeterminant state behind after stack unrolling. The app then fails with heisenbugs later, raising more exceptions that get ignored, compounding the problem.
People just shrug off that unreliability as an unavoidable cost of doing business.
Yeah, in both cases it's a layering situation, where it's the duty of your code to decide what layers of abstraction need to be be bridged, and to execute on that decision. Translating/wrapping exception-types from deeper functions is the same as translating/wrapping return-types the same places.
I think it comes down to a psychological or use-case issue: People hate thinking about errors and handling them, because it's that hard stuff that always consumes more time than we'd like to think. Not just digitally, but in physical machines too. It's also easier to put off "for later."
Checked exceptions in theory were good, but Java simply did not add facilities to handle or support them well in many APIs. Even the new API's in Java - Streams, etc do not support checked exceptions.
There is also the problem that they decided to make all references nullable, so `NullPointerException`s could appear everywhere. This "forced" them to introduce the escape hatch of `RuntimeException`, which of course was way overused immediately, normalizing it.
It's a lot lighter: a stack trace takes a lot of overhead to generate; a result has no overhead for a failure. The overhead (panic) only comes once the failure can't be handled. (Most books on Java/C# don't explain that throwing exceptions has high performance overhead.)
Exceptions force a panic on all errors, which is why they're supposed to be used in "exceptional" situations. To avoid exceptions when an error is expected, (eof, broken socket, file not found,) you either have to use an unnatural return type or accept the performance penalty of the panic that happens when you "throw."
In Rust, the stack trace happens at panic (unwrap), which is when the error isn't handled. IE, it's not when the file isn't found, it's when the error isn't handled.
Exceptions do not force panic at all. In most practical situations, an exception unhandled close to where it was thrown will eventually get logged. It's kind of a "local" panic, if you will, that will terminate the specific function, but the rest of the program will remain unaffected. For example, a web server might throw an exception while processing a specific HTTP request, but other HTTP requests are unaffected.
Throwing an exception does not necessarily mean that your program is suddenly in an unsupported state, and therefore does not require terminating the entire program.
> Throwing an exception does not necessarily mean that your program is suddenly in an unsupported state, and therefore does not require terminating the entire program.
That's not what a panic means. Take a read through Go's panic / resume mechanism; it's similar to exceptions, but the semantics (with multiple return values) make it clear that panic is for exceptional situations. (IE, panic isn't for "file not found," but instead it's for when code isn't written to handle "file not found.")
Sure, but the same is true of any error handling strategy.
When you work with exceptions, the key is to assume that every line can throw unless proven otherwise, which in practice means almost all lines of code can throw. Once you adopt that mental model, things get easier.
Explicit error handling strategies allow you to not worry about all the code paths that explicitly cannot throw -- which is a lot of them. It makes life a lot easier in the non-throwing case, and doesn't complicate life any more in the throwing case as compared to exception-based error handling.
It also makes errors part of the API contract, which is where they belong, because they are.
It can and that optimization has existed for a while.
Actually it can also just turn off the collection of stack traces entirely for throw sites that are being hit all the time. But most Java code doesn't need this because code only throws exceptions for exceptional situations.
> it's essentially a checked exception without a stack trace
In theory, theory and practice are the same. In practice...
You can't throw a checked exception in a stream, this fact actually underlines the key difference between an exception and a Result: Result is in return position and exceptions are a sort of side effect that has its own control flow. Because of that, once your method throws an Exception or you are writing code in a try block that catches an exception, you become blind to further exceptions of that type, even if you might be able to or required to fix those errors. Results are required to be handled individually and you get syntactic sugar to easily back propagate.
It is trivial to include a stack trace, but stack traces are really only useful for identifying where something occurred, and generally what is superior is attaching context as you back propagate which trivially occurs with judicious use of custom error types with From impls. Doing this means that the error message uniquely defines the origin and paths it passed through without intermediate unimportant stack noise. With exceptions you would always need to catch each exception and rethrow a new exception containing the old to add contextual information, then to avoid catching to much you need variables that will be initialized inside the try block defined outside of the try block. So stack traces are basically only useful when you are doing Pokemon exception handling.
> When Rust got popular, I was a bit confused by people talking about how great Result it's essentially a checked exception without a stack trace.
It's not a checked exception without a stack trace.
Rust doesn't have Java's checked or unchecked exception semantics at the moment. Panics are more like Java's Errors (e.g. OOM error). Results are just error codes on steroids.
checked exceptions failed because when used properly they fossilize method signatures. they're fine if your code will never be changed and they're fine when you control 100% of users of the throwing code. if you're distributing a library... no bueno.
That’s just not true. They required that you use hierarchical exception types and define your own library exception type that you declare at the boundary.
The same is required for any principled error handling.
