Parameter borrows should happen before receiver borrows

[jethrogb]

This works:

fn main() {
    let mut nums=vec![10i,11,12,13];
    let index=nums.len()-2;
    *nums.get_mut(index)=2;
}

I would like to be able to write this instead:

fn main() {
    let mut nums=vec![10i,11,12,13];
    *nums.get_mut(nums.len()-2)=2;
}

But:

test.rs:3:16: 3:20 error: cannot borrow `nums` as immutable because it is also borrowed as mutable
test.rs:3   *nums.get_mut(nums.len()-2)=2;
                          ^~~~
test.rs:3:3: 3:7 note: previous borrow of `nums` occurs here; the mutable borrow prevents subsequent moves, borrows, or modification of `nums` until the borrow ends
test.rs:3   *nums.get_mut(nums.len()-2)=2;
             ^~~~

Lexically, the receivers appears before the parameters, but semantically it appears later, which is when I'd expect the borrow to happen.

[thestinger]

cc @nikomatsakis

I think this is likely a duplicate of an existing issue.

[jethrogb]

I think #6393 is related but not quite the same.

[ftxqxd]

Isn’t this #6268?

[jethrogb]

"receivers" was the word I was looking for earlier, thank you!

#6268 isn't quite the same, that ticket is about mutable receivers, while here I'm using an immutable receiver as a parameter. Would love for #6268 to get fixed though :)

Edit: on closer inspection, the first example in #6268 is in fact the same as this, but the bug title seems to be more general.

[huonw]

Closing as a dupe of #6268. Thanks for filing! (That issue is more general: we don't necessary want to take the specific solution suggested in the title of this issue. Maybe we do, but in any case, #6268 is the underlying cause.)