Field Init Shorthand Uses a Matching Variable Name

When a field and a variable have the same name, Rust lets us write that name once in a struct literal. Writing width there is shorthand for width: width in source.

struct Rectangle {
    width: u32,
    height: u32,
}
 
fn make_rectangle(width: u32, height: u32) -> Rectangle {
    Rectangle { width, height }
}
 
fn main() {
    let rectangle = make_rectangle(30, 50);
    println!("{} by {}", rectangle.width, rectangle.height);
}

So, the function receives variables named width and height and the struct has fields with those names, so Rectangle {width, height} fills both the fields from the variables. It creates the same vale as Rectangle { width: width, height: height }

you can try to change the parameter name from width to new_width without changing the struct literal, now if you’ll do cargo check it can’t find a variable named width. Write width: new_width and it’ll work again