37 lines
1004 B
Rust
37 lines
1004 B
Rust
struct Point { x: isize, y: isize }
|
|
|
|
fn a() {
|
|
let mut p = Point {x: 3, y: 4};
|
|
let q = &p;
|
|
|
|
// This assignment is illegal because the field x is not
|
|
// inherently mutable; since `p` was made immutable, `p.x` is now
|
|
// immutable. Otherwise the type of &_q.x (&isize) would be wrong.
|
|
p.x = 5; //~ ERROR cannot assign to `p.x` because it is borrowed
|
|
q.x;
|
|
}
|
|
|
|
fn c() {
|
|
// this is sort of the opposite. We take a loan to the interior of `p`
|
|
// and then try to overwrite `p` as a whole.
|
|
|
|
let mut p = Point {x: 3, y: 4};
|
|
let q = &p.y;
|
|
p = Point {x: 5, y: 7};//~ ERROR cannot assign to `p` because it is borrowed
|
|
p.x; // silence warning
|
|
*q; // stretch loan
|
|
}
|
|
|
|
fn d() {
|
|
// just for completeness's sake, the easy case, where we take the
|
|
// address of a subcomponent and then modify that subcomponent:
|
|
|
|
let mut p = Point {x: 3, y: 4};
|
|
let q = &p.y;
|
|
p.y = 5; //~ ERROR cannot assign to `p.y` because it is borrowed
|
|
*q;
|
|
}
|
|
|
|
fn main() {
|
|
}
|