How can I set the array values to 0 in this struct? This is obviously wrong. How do I do it correctly?
struct Game {
board: [[i32; 3]; 3] = [[0, 0, 0], [0, 0, 0], [0, 0, 0]];
}
In a function this would have been:
let board: [[i32; 3]; 3] = [[0, 0, 0], [0, 0, 0], [0, 0, 0]];
You cannot initialize fields in struct definition because it is behaviour while struct must contain only data.
This should work:
struct Game {
board: [[i32; 3]; 3]
}
impl Game{
fn new()->Self{
Self{
board: [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
}
}
}
...
let game = Game::new();
If you want to define a default value for a struct, you can implement the Default trait for it.
In the case of a struct containing values that themselves implement Default, it is as simple as adding #[derive(Default)]:
#[derive(Default,Debug)]
struct Game {
board: [[i32; 3]; 3]
}
fn main() {
let game : Game = Default::default();
println!("{:?}", game);
}
Alternatively, if your struct is more complex, you can implement Default by hand.
The advantage of using Default over writing a constructor (as in Angelicos' answer) is that:
derive to implement itderive..Default::default() struct update syntax to specify some fields of a struct, while defaulting the rest.See also:
Default and new() in libraries. For apps, I tend to have only Default but this is opinion-based
S{f1, f2, ..S::new()}. Actually, you can use any expression which returns this struct.
Default::default()for default values (0 for integers) or array initialization syntax for any other constant value ([[0; 3]; 3])