| // Copyright 2012 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| 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` |
| 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` |
| 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` |
| *q; |
| } |
| |
| fn main() { |
| } |