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January 8, 2017 22:50
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Rust for the Experienced Programmer. Lesson 2: references vs values
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| #[derive(Debug)] | |
| struct Person { | |
| id: u64, | |
| name: String, | |
| } | |
| impl Person { | |
| // Because we're passing a value, we take ownership of it. If we want to give | |
| // ownership back, we have to return it. | |
| fn set_name(mut self, new_name: String) -> Person { | |
| self.name = new_name; | |
| return self; | |
| } | |
| // Since we're borrowing a reference, we don't take ownership. | |
| fn name_with_greeting(&self) -> String { | |
| return "Greetings, ".to_string() + self.name.as_str(); | |
| } | |
| // By taking a mutable reference, we can change it and not have to return | |
| // it. The rule: the compiler will only hand out a single mutable reference | |
| // at once. | |
| fn set_name2(&mut self, new_name: String) { | |
| // This is automatically deferenced by Rust. | |
| self.name = new_name; | |
| } | |
| } | |
| fn main() { | |
| // Since we're planning to change a field, we have to mark this as mutable | |
| let mut stevej = Person { | |
| id: 1, | |
| name: "Steve Jenson".to_string(), | |
| }; | |
| stevej.name = "Stan Jergsen".to_string(); | |
| println!("{:?}", stevej); | |
| // This is a common Rust idiom where ownership changes are handled by | |
| // using assignment. Let's walk through why. | |
| let mut stevej = stevej.set_name("Frob Johnson".to_string()); | |
| println!("{:?}", stevej); | |
| println!("{:?}", stevej.name_with_greeting()); | |
| stevej.set_name2("Ferg Johannsen".to_string()); | |
| // Because set_name2 takes a reference, a borrow happened instead of | |
| // an ownership change. | |
| println!("{:?}", stevej); | |
| } |
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https://play.rust-lang.org/?gist=100479ca8dea0495070a2f754537ad02