Closed
Description
When I have a struct with two methods on the impl, both borrowing self mutably, I cannot chain the functions, like s.second(s.first()): I get a borrow checker error. Instead, I have to assign s.first() to an auxiliary variable. Might be related to #21906 but could not find any other similar issues.
struct S{}
impl S{
fn first(&mut self) -> bool{
true
}
fn second(&mut self, b: bool) {
if b { println!{"Hello, world!"}; }
}
}
fn main() {
let mut s = S{};
s.second(s.first());
}I expected to see this happen: a simple print of "hello world!"
Instead, this happened:
Compiling playground v0.0.1 (/playground)
error[E0499]: cannot borrow `s` as mutable more than once at a time
--> src/main.rs:15:14
|
15 | s.second(s.first())
| - ------ ^ second mutable borrow occurs here
| | |
| | first borrow later used by call
| first mutable borrow occurs here
error: aborting due to previous error
For more information about this error, try `rustc --explain E0499`.
error: could not compile `playground`
To learn more, run the command again with --verbose.
It works fine if we use an auxiliary variable, which looks quite ugly to my mind:
fn main() {
let mut s = S{};
let f = s.first();
s.second(s.first());
}