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