Rust
Field update
Move fields from one struct to another with the .. syntax.
Struct update syntax
To copy most fields of an existing instance and change only some, ..kaynak is used; it's always written last:
let a = Oyuncu { ad: String::from("Ece"), puan: 10, aktif: true };
let b = Oyuncu { ad: String::from("Can"), ..a };
println!("{} {}", b.ad, b.puan); // Can 10
Here puan and aktif are Copy types, so they are copied; a is still fully usable.
Partial moves
Only some fields of a struct can be moved; this is called a partial move. Access to the moved field and to the whole instance is forbidden; the remaining fields can be used:
let a = Oyuncu { ad: String::from("Ece"), puan: 10, aktif: true };
let b = Oyuncu { puan: 99, ..a };
println!("{}", a.puan); // fine: Copy
// println!("{}", a.ad); // error E0382
// let c = a; // error: a was partially moved
To avoid the move, you can write ..a.clone() (the struct must derive Clone).
Exercise Derive a new player
Define Oyuncu { ad: String, puan: u32, aktif: bool }. Let a be Ece, 10, true. Create b with ad: "Can" and ..a. Print b.ad, b.puan, b.aktif and a.ad separated by spaces.
Show example solution
struct Oyuncu {
ad: String,
puan: u32,
aktif: bool,
}
fn main() {
let a = Oyuncu {
ad: String::from("Ece"),
puan: 10,
aktif: true,
};
let b = Oyuncu {
ad: String::from("Can"),
..a
};
println!("{} {} {} {}", b.ad, b.puan, b.aktif, a.ad);
}
Test yourself
-
After <code>let b = Oyuncu { puan: 99, ..a };</code>, can <code>a.ad</code> be used?
- Yes, it was copied
- Yes, it was borrowed
- b can't be created
- No: ad (a String) was moved into b
Show answer
No: ad (a String) was moved into b — ..a moves the fields not given. Since String isn't Copy, a.ad is no longer valid (a.puan and a.aktif can still be used).
-
Copy the rest
let b = Oyuncu {
ad: String::from("Can"),
____
};
Show answer
let b = Oyuncu {
ad: String::from("Can"),
..a
};
-
Case and result
- { ad: yeni, ..a } then a.ad
- Usable
- { puan: 1, ..a } then a.ad
- E0382
- { puan: 1, ..a } then a.puan
- Usable (Copy)
- ..a.clone()
- No move
Next lesson: Summary - Structs
