2.9 KiB
2.9 KiB
Reference and Borrowing
Reference
- π
fn main() {
let x = 5;
// fill the blank
let p = __;
println!("the memory address of x is {:p}", p); // one possible output: 0x16fa3ac84
}
- π
fn main() {
let x = 5;
let y = &x;
// modify this line only
assert_eq!(5, y);
println!("Success!")
}
- π
// fix error
fn main() {
let mut s = String::from("hello, ");
borrow_object(s);
println!("Success!")
}
fn borrow_object(s: &String) {}
- π
// fix error
fn main() {
let mut s = String::from("hello, ");
push_str(s);
println!("Success!")
}
fn push_str(s: &mut String) {
s.push_str("world")
}
- ππ
fn main() {
let mut s = String::from("hello, ");
// fill the blank to make it work
let p = __;
p.push_str("world");
println!("Success!")
}
ref
ref
can be used to take references to a value, similar to &
.
- πππ
fn main() {
let c = 'δΈ';
let r1 = &c;
// fill the blankοΌdont change other code
let __ r2 = c;
assert_eq!(*r1, *r2);
// check the equality of the two address strings
assert_eq!(get_addr(r1),get_addr(r2));
println!("Success!")
}
// get memory address string
fn get_addr(r: &char) -> String {
format!("{:p}", r)
}
Borrowing rules
- π
// remove something to make it work
// don't remove a whole line !
fn main() {
let mut s = String::from("hello");
let r1 = &mut s;
let r2 = &mut s;
println!("{}, {}", r1, r2);
println!("Success!")
}
Mutablity
- π Error: Borrow a immutable object as mutable
fn main() {
//fix error by modifying this line
let s = String::from("hello, ");
borrow_object(&mut s);
println!("Success!")
}
fn borrow_object(s: &mut String) {}
- ππ Ok: Borrow a mutable object as immutable
// this code has no errors!
fn main() {
let mut s = String::from("hello, ");
borrow_object(&s);
s.push_str("world");
println!("Success!")
}
fn borrow_object(s: &String) {}
NLL
- ππ
// comment one line to make it work
fn main() {
let mut s = String::from("hello, ");
let r1 = &mut s;
r1.push_str("world");
let r2 = &mut s;
r2.push_str("!");
println!("{}",r1);
}
- ππ
fn main() {
let mut s = String::from("hello, ");
let r1 = &mut s;
let r2 = &mut s;
// add one line below to make a compiler error: cannot borrow `s` as mutable more than once at a time
// you can't use r1 and r2 at the same time
}
You can find the solutions here(under the solutions path), but only use it when you need it