rust/src/test/compile-fail/borrowck/borrowck-assign-comp.rs
2016-02-24 18:40:39 -05:00

47 lines
1.4 KiB
Rust

// 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() {
}