In older Rust, when initializing a struct, you must always give the full set of key: value pairs for its fields:

#![allow(unused_variables)]
fn main() {
struct Point {
    x: i32,
    y: i32,
}

let a = 5;
let b = 6;

let p = Point {
    x: a,
    y: b,
};
}

However, often these variables would have the same names as the fields. So you'd end up with code that looks like this:

let p = Point {
    x: x,
    y: y,
};

Now, if the variable is of the same name, you don't have to write out both, just write out the key:

#![allow(unused_variables)]
fn main() {
struct Point {
    x: i32,
    y: i32,
}

let x = 5;
let y = 6;

// new
let p = Point {
    x,
    y,
};
}