In Rust, you can create a new instance of a struct that includes most of the values from another instance but changes some using the struct update syntax. This allows you to update specific fields while keeping the remaining fields the same as the original instance. Here's an example:
struct User {
active: bool,
username: String,
email: String,
sign_in_count: u64,
}
fn main() {
let user1 = User {
active: true,
username: String::from("john_doe"),
email: String::from("john@example.com"),
sign_in_count: 1,
};
let user2 = User {
email: String::from("another@example.com"),
..user1
};
println!("user1: {:?}", user1);
println!("user2: {:?}", user2);
}
In this example, we have a `User` struct with four fields: `active`, `username`, `email`, and `sign_in_count`. We create an instance `user1` with initial values. To create a new instance `user2` based on `user1` with an updated email, we use the struct update syntax.
The line `..user1` specifies that the remaining fields in `user2` should have the same values as the corresponding fields in `user1`. In this case, `active`, `username`, and `sign_in_count` fields will be copied from `user1`, while the `email` field will be updated to `"another@example.com"`.
Note that the struct update syntax moves the data from the original instance, just like an assignment. Therefore, you can no longer use `user1` after creating `user2`. If you want to reuse `user1` afterwards, you can provide new values for both `email` and `username` fields in `user2`, ensuring that only the fields you explicitly update are moved.
Also, it's worth mentioning that fields that implement the `Copy` trait, such as `bool` and `u64` in this example, will be copied instead of moved.
