45 lines
1.3 KiB
Rust
45 lines
1.3 KiB
Rust
type point = { x: int, y: int };
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fn a() {
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let mut p = {x: 3, y: 4};
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let _q = &p; //~ NOTE loan of mutable local variable granted here
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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 (&int) would be wrong.
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p.x = 5; //~ ERROR assigning to mutable field prohibited due to outstanding loan
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}
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fn b() {
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let mut p = {x: 3, mut y: 4};
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let _q = &p;
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// This assignment is legal because `y` is inherently mutable (and
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// hence &_q.y is &mut int).
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p.y = 5;
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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 = {x: 3, mut y: 4};
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let _q = &p.y; //~ NOTE loan of mutable local variable granted here
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p = {x: 5, mut y: 7};//~ ERROR assigning to mutable local variable prohibited due to outstanding loan
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copy p;
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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 = {x: 3, mut y: 4};
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let _q = &p.y; //~ NOTE loan of mutable field granted here
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p.y = 5; //~ ERROR assigning to mutable field prohibited due to outstanding loan
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copy p;
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}
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fn main() {
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}
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