I'm not sure why you put 'safe' in quotes here; nothing about 'unwrap()' (or even 'panic') is unsafe in the context of Rust. In fact, it acts just like Python would in the same circumstances: print a developer-centric message out and exit with a bad return code.
What's unsafe about that?
> if you're gonna have unwrap, you basically have to have exceptions as well
Why do you think that? unwrap() is meant to be the same as throwing an uncatchable exception; if you want to throw an exception that you mean to catch somewhere, you should be using something else.
> people prefer to use [unwrap()] than use the verbose match statement
People may not be aware (which will come with time) but there are more than just those two choices when it comes to error handling in Rust.
Unwrap is a shortcut to let you be lazy; it exists for no other reason, and it causes application level crashes in way that is very much easier to avoid in other languages.
That 'catch_unwind' exists is evidence that some kind of panic recovery is necessary... and I wonder how often you hit it from a real panic, vs. a stray lazy unwrap?
Whats your justification for unwrap? I've never seen a meaningful justification for it other than not wanting to handle errors properly.
An application error (returned null) shouldn't abort your application with a hard error, no logs. Its just plain poor practice to use unwrap().
Your phrasing implied that you said the crash was not safe, as you put "unsafe" in quotes and contrasted it with the crash. At least, that's what I understood you to be saying too.
I feel like any time someone mentions the word 'safe' regardless of context, the rust safety pedants roll out of the woodwork to dispute to dispute any minute detail of what's been said, regardless of if its relevant to the discussion at hand. I shouldn't have put 'safe' in the comment at all, what a waste of a thread.
My point had nothing to do with safety; it was purely that having given advice being to write good code that doesn't panic, and then having code that shamelessly panics in all your examples is hypocritical.
`?` is a better choice in basically every case; I'm glad to see the documentation will be moving eventually towards using that.
Panics mostly match the verbosity, ergonomics, and functionality of the analogous python script.
Now I agree that a caveat should follow advice like using unwrap and expect, perhaps a small blurb about how they should eschewed for better error handling when you want to catch the errors and make decisions because of them (especially when writing libraries) but that's quite a bit short of hypocritical to me.
That is literally the definition of hypocrisy; the behavior of people who do things that they tell other people not to do.
"When you do this, do it like this, but properly with error handling." :P
Anyhow, as I said its my oppinion that unwrap() is lazy, and `?`, `expect` and `assert!` cover the same functionality in more explicit and meaningful way.
You're welcome to your own opinion.
Except I'm not saying that at all.
I said it's fine to use unwrap() or expect() if you want script-like default behavior (a developer-centric error message and a quick exit with a bad return code) and if you want something more than that, then use something better than unwrap() or expect().
There's no hypocrisy here. I think anyone should follow that advice. Me, you, a newb to Rust, a Rust veteran, anyone. Same advice.
What? That's what every other language does.
file.open("foo").read_line()
Though it might be interesting if there was a special opt-in Deref impl for Result and Option so people could omit the unwrap and just get it implicitly, for the occasions when you don't want that explicitness.
Unwrap does what just about every other language with exceptions-by-default does: it prints out a message for developers and exits. If you don't want that behavior, that's fine; in Rust you'd not use unwrap(), and in other languages you'd catch the exception.
Now, I agree that if you are using a library which does unwrap() in Rust vs a library that throws an exception in Python, you have different situations. But unwrap() isn't meant to be used in libraries (or if it is, only for fatal errors which should be uncatchable).
> Whats (sic) your justification for unwrap? I've never seen a meaningful justification for it other than not wanting to handle errors properly.
That is the justification for it: you are writing a simple short script-like tool (or you are prototyping or exploring some problem through one-off or throw-away code) and you want any errors to immediately exit with a developer-centric message and failure code. unwrap() is perfect for this.
It's the same justification for not catching every exception in other languages. Sometimes you are fine with an error printing a message and exiting.
It might crash, but it doesn't burn, which is kinda the point of panic. Its behavior is well defined and predictable, which is great improvement over typical C UB.
But speaking about blogs... Why not to use .unwrap() there? Its simple, and allows to show some ideas without digging into error handling, just point to places where those handling should be placed.
> but if you're gonna have unwrap, you basically have to have exceptions as well (or some kind of panic recovery) ...
https://doc.rust-lang.org/1.9.0/std/panic/fn.catch_unwind.ht...
...because people use it; and then say; 'but don't use unwrap...'; and then use it, and your 'safe' language then happily crashes and burns everytime something goes wrong.
Blogs and documentation are particularly prone to it.
Result and option types are good; but if you're gonna have unwrap, you basically have to have exceptions as well (or some kind of panic recovery), because, people prefer to use it than use the verbose match statement. :/