Example
#[derive(Debug)] struct Race { name: String, laps: Vec<i32>, } impl Race { fn new(name: &str) -> Race { // No receiver, a static method Race { name: String::from(name), laps: Vec::new() } } fn add_lap(&mut self, lap: i32) { // Exclusive borrowed read-write access to self self.laps.push(lap); } fn print_laps(&self) { // Shared and read-only borrowed access to self println!("Recorded {} laps for {}:", self.laps.len(), self.name); for (idx, lap) in self.laps.iter().enumerate() { println!("Lap {idx}: {lap} sec"); } } fn finish(self) { // Exclusive ownership of self let total = self.laps.iter().sum::<i32>(); println!("Race {} is finished, total lap time: {}", self.name, total); } } fn main() { let mut race = Race::new("Monaco Grand Prix"); race.add_lap(70); race.add_lap(68); race.print_laps(); race.add_lap(71); race.print_laps(); race.finish(); // race.add_lap(42); }
Key Points:
- All four methods here use a different method receiver.
- You can point out how that changes what the function can do with the variable values and if/how it can be used again in
main
. - You can showcase the error that appears when trying to call
finish
twice.
- You can point out how that changes what the function can do with the variable values and if/how it can be used again in
- Note, that although the method receivers are different, the non-static functions are called the same way in the main body. Rust enables automatic referencing and dereferencing when calling methods. Rust automatically adds in the
&
,*
,muts
so that that object matches the method signature. - You might point out that
print_laps
is using a vector that is iterated over. We describe vectors in more detail in the afternoon.