Reference and Borrowing
Reference
- 🌟
fn main() { let x = 5; // fill the blank let p = __; println!("the memory address of x is {:p}", p); // one possible output: 0x16fa3ac84 }
- 🌟
fn main() { let x = 5; let y = &x; // modify this line only assert_eq!(5, y); println!("Success!") }
- 🌟
// fix error fn main() { let mut s = String::from("hello, "); borrow_object(s); println!("Success!") } fn borrow_object(s: &String) {}
- 🌟
// 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") }
- 🌟🌟
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 &
.
- 🌟🌟🌟
fn main() { let c = '中'; let r1 = &c; // fill the blank,dont 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
- 🌟
// 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
- 🌟 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) {}
- 🌟🌟 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
- 🌟🌟
// 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); }
- 🌟🌟
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