从Rust的Ordering :: *到整数有内置的转换吗？

Question

To increment or decrement something based on whether it's below or above some other value, I can do this:

if destination > self.position {
    self.position += 1;
} else if destination < self.position {
    self.position -= 1;
}

or this:

self.position += match self.position.cmp(&destination) {
    Ordering::Less => {
        1
    }
    Ordering::Greater => {
        -1
    }
    Ordering::Equal => {
        0
    }
}

The latter is IMO clearer, but much more verbose. Is there a way convert these Ordering values to integers (-1, 0, 1), similar to PHP's spaceship operator , or otherwise reduce the verbosity of this code?

Answer 1

Yes, you can cast them to signed integers (which can be verified in the source of cmp::Ordering ):

use std::cmp::Ordering;

fn main() {
    println!("{}", Ordering::Less as i8);    // -1
    println!("{}", Ordering::Equal as i32);   // 0
    println!("{}", Ordering::Greater as i64); // 1
}

In your case this could be used as follows:

self.position -= self.position.cmp(&destination) as i8; // or a different, more suitable signed integer

Answer 2

Like @ljedrz said, you can convert the Ordering to an integer. Another option, which may be clearer is to remember that you can use if as an expression:

self.position += if destination > self.position      {  1 }
                 else if destination < self.position { -1 }
                 else                                {  0 };