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