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Borrowck doesn't handle &mut correctly anymore #3765

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nikomatsakis opened this issue Oct 14, 2012 · 1 comment
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Borrowck doesn't handle &mut correctly anymore #3765

nikomatsakis opened this issue Oct 14, 2012 · 1 comment
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A-lifetimes Area: Lifetimes / regions I-crash Issue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.
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@nikomatsakis
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This USED to be an error, but doesn't seem to be anymore:

use core::either::{Either, Left, Right};

    fn f(x: &mut Either<int,float>, y: &Either<int,float>) -> int {
        match *y {
            Left(ref z) => {
                *x = Right(1.0);
                *z
            }
            _ => fail
        }
    }

    fn main() {
        let mut x: Either<int,float> = Left(3);
        io::println(f(&mut x, &x).to_str());
    } 

In particular it should not be allowed to simultaneously have an &mut and an & in scope. I recall that I changed the rules at some point around the creation of &mut pointers—that used to be considered equivalent to writing to the variable in question. I should not have changed that rule!

@nikomatsakis
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Oh, this isn't quite the bug I thought it was. This has to do with the compatible loan check. It checks that new loans are compatible with old loans but not that new loans are compatible with each other. Got a fix, testing now.

nikomatsakis added a commit to nikomatsakis/rust that referenced this issue Oct 14, 2012
Along the way, convert from dvec-of-dvec representation to track loans in scope
to just a single flattened list.  It's more convenient.

No review: small bug fix.

Fixes rust-lang#3765.
RalfJung pushed a commit to RalfJung/rust that referenced this issue Jul 29, 2024
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Labels
A-lifetimes Area: Lifetimes / regions I-crash Issue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.
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