43 lines
1.2 KiB
Rust
43 lines
1.2 KiB
Rust
// revisions: ast mir
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//[mir]compile-flags: -Z borrowck=mir
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struct Point { x: isize, y: isize }
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fn a() {
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let mut p = Point {x: 3, y: 4};
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let q = &p;
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// This assignment is illegal because the field x is not
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// inherently mutable; since `p` was made immutable, `p.x` is now
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// immutable. Otherwise the type of &_q.x (&isize) would be wrong.
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p.x = 5; //[ast]~ ERROR cannot assign to `p.x`
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//[mir]~^ ERROR cannot assign to `p.x` because it is borrowed
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q.x;
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}
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fn c() {
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// this is sort of the opposite. We take a loan to the interior of `p`
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// and then try to overwrite `p` as a whole.
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let mut p = Point {x: 3, y: 4};
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let q = &p.y;
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p = Point {x: 5, y: 7};//[ast]~ ERROR cannot assign to `p`
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//[mir]~^ ERROR cannot assign to `p` because it is borrowed
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p.x; // silence warning
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*q; // stretch loan
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}
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fn d() {
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// just for completeness's sake, the easy case, where we take the
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// address of a subcomponent and then modify that subcomponent:
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let mut p = Point {x: 3, y: 4};
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let q = &p.y;
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p.y = 5; //[ast]~ ERROR cannot assign to `p.y`
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//[mir]~^ ERROR cannot assign to `p.y` because it is borrowed
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*q;
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}
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fn main() {
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}
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