// https://google.github.io/comprehensive-rust/ownership/lifetimes-function-calls.html
#[derive(Debug)]
struct Point(i32, i32);

// 'a is a generic parameter, it is inferred by the compiler.
// Lifetimes start with ' and 'a is a typical default name.
// Read &'a Point as “a borrowed Point which is valid for at least the lifetime a”.
// The at least part is important when parameters are in different scopes.
fn left_most<'a>(p1: &'a Point, p2: &'a Point) -> &'a Point {
    if p1.0 < p2.0 { p1 } else { p2 }
}

fn main() {
    let p1: Point = Point(10, 10);
    let p2: Point = Point(20, 20);  // Put into different scope
    let p3: &Point = left_most(&p1, &p2);
    println!("left-most point: {:?}", p3);
}