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Document universal &mut reborrows - #2373
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| If the type of that value implements [`Copy`], then the value will be copied. | ||
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| r[expr.move.mut-ref] | ||
| If the type of that value is `&mut T`, and the place expression is mutable, then the value will be reborrowed. This is equivalent to applying `&mut *` (a [dereference][deref] and then a [mutable borrow][borrow]) to the place. |
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What do you make of this example (the first example in the stabilization report) under the rule? How would we justify the reborrow here?
fn generic(_: impl Sized) {}
let x = &mut ();
generic(x);
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The x in generic(x) is a "place expression in value expression context" with type &mut.
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The rule as written requires that the place expression be mutable, and x is not a mutable place expression.
(Perhaps it means to say, e.g., that a dereference of the place expression be mutable?)
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It should be "mutable or movable". Fixed
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What do you make of this, which is accepted by your PR but rejected by the rule?
struct S<'a>(&'a mut u8);
impl Drop for S<'_> { fn drop(&mut self) {} }
fn f(x: S<'_>) {
let y = x.0; // ERROR or OK?
*y = 1;
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Good point. The current wording of the Reference concerning Drop isn't even grammatically correct lol (matches a singular with a plural). I've changed this again to just re-use the wording from expr.deref.mut
Re-use phrasing from expr.deref.mut
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Documents rust-lang/rust#163494.