Rust: What the fuck is a borrow checker and why is it yelling at me?

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > Rust: What the fuck is a borrow checker and why is it yelling at me?

QuantumNinja: Mar 8, 2013; Trust me.
I pretend to be a ninja.

I'd write it more like:

code:

            Dest::Register(r) => self.v.get_mut(r)
                                       .and_then(|reg| { *reg = data as Register8 & 0xFF; Some(())} )
                                       .ok_or(Err(Chip8Error::OutOfBoundsAt(r))),
...
            Src::Register(r)  => self.v.get(r)
                                       .and_then(|reg| *reg as usize)
                                       .ok_or(Chip8Error::OutOfBoundsAt(r)),

That said, the Dest register thing seems a bit like a misuse of the Result type. Do you plan to catch and handle that Chip8Error? If not, use a panic!. If you do, a Result containing a unit on one side is an Option, and it would probably be nicer to just write update_reg(reg: Reg, index: usize) -> Option<Chip8Error> and call that.

QuantumNinja fucked around with this message at 06:13 on Jul 28, 2016

# ¿ Jul 28, 2016 06:10

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# ¿ May 3, 2024 08:59

QuantumNinja: Mar 8, 2013; Trust me.
I pretend to be a ninja.

taqueso posted:

I don't want to panic inside my library for a minor error like this. I'm trying to pass the results all the way out to the API boundary so the calling app can see & handle the errors. I considered using Option here, but didn't use it for 2 reasons - I read somewhere that it was bad form to use None to indicate an error condition, and also so I don't have to convert the Option to a Result in the calling functions. This is pretty analogous to std's use of None when popping from a collection, so it is mostly for the second reason.

The library is pretty functional now, I'll try to post the code later today.

I agree that panic! is probably too much. But I wasn't advocating None as Error, I was advocating None as the unit result, where you only get something back if you have an error. For the sort of thing you seem to have here, though, I agree that following the Option conventions of std::Vec is probably a good best-practices guideline. :shrug:

Vanadium posted:

Result<(), T> is a legit pattern.

You see it in std::fmt and the serialzied, and a few other places, but it's never carried very far in those APIs. taqueso's snippet sort of implies that it's going to carry a Result<(), T> through a few layers to "propagate the error", though, and that's going to induce a nasty ok_or chain all the way up the callstack.

# ¿ Jul 28, 2016 19:03

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > Rust: What the fuck is a borrow checker and why is it yelling at me?