Does a mutable reference means an ownership loss in Rust?

Question

This exercice from Rustlings, once corrected, gives:

 fn move_semantics4() { let mut x = Vec::new(); let y = &mut x; y.push(42); let z = &mut x; z.push(13); assert_eq!(x, [42, 13]); }

If I put it through Aquascope, on the borrow checker, it gives:

I don't understand why x is loosing ownership on L3 and L5. AFAIK, the mutable reference assignated to y and z implies:

No more reference can be created on x (only one mutable reference at a time)
Ability for y and z (sequentially) to read and write on vector

But not loosing ownership.

According to me, visual representation seems validating the ownership staying on x:

Could someone elaborate on this?

EDIT: for the sake of completness, I created another snippet with both move and mutable reference, and there is a special char (fat arrow) when a move is made :

No. x keeps being the owner of the Vec during the entire snippet. — user22747722
– user22747722, Commented Aug 21, 2024 at 10:00
I visited that Aquascope site, and I could not find any key on the site defining what O (or W and R) stand for. — user22747722
– user22747722, Commented Aug 21, 2024 at 10:05

Alexey S. Larionov · Accepted Answer · 2024-08-21 10:35:14Z

On Aquascope website, you can hover the pictograms like +R/-R/+W/-W/+O/-O and arrows like →, and it shows a popup tooltip on the meaning (the same can be also viewed in raw HTML tree).

In particular, it shows:

+O Path did not have own permissions before the preceding line, and gained it after this line"

-O Path had own permissions before the preceding line, and lost it after this line.

→ Path is borrowed here

So after all, line 3, the action on x → -O can be understood as x is borrowed here, and "loss of own permission" doesn't mean that x no longer owns the object, it means that it can no longer transfer ownership to anybody, because a borrowing exists. Meanwhile, y → +O means that y object is instantiated, but it's a reference, and it can do ownership transfer of the reference, not the referenced object.

On line 4, the lifetime of y ends, it's destroyed, thus x → +O received the ability to transfer the ownership (though it always held the ownership)

Collectives™ on Stack Overflow

Does a mutable reference means an ownership loss in Rust?

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related