Rust struct field order

Part of the “Rustober” series.

One of the Rust quirks is that when initializing a struct, the named fields can be in any order:

struct Point {
    first: i32,
    second: i32,
    third: i32,
}

let p = Point { third: 1, second: 2, first: 3 };

In Swift, this is an error. However, looking at the rules for C initialization, it seems the C behavior is the same, called “designated initializer” and has been available since C99. Possibly, this also has to deal with Rust’s struct update syntax where you can initialize a struct based on another instance, in which case the set of field names would be incomplete, so their order does not really matter since they are named:

// Use values from p but change .third to 3
let p2 = Point {
    third: 3,
    ..p
};