How to convert generic primitive types in rust? [d

问题:

This question already has an answer here:

How to cast generic types that I know to be integers? (1 answer)

Closed 11 months ago.

I would like to write something like the following in rust:

pub struct Point<T> {
    pub x: T,
    pub y: T,
}

impl<T> Point<T> {
    pub fn from<U>(other: Point<U>) -> Point<T> {
        Point {
            x: other.x as T,
            y: other as T,
        }
    }
}

This is not possible:

error[E0605]: non-primitive cast: `U` as `T`
 --> src/lib.rs:9:16
  |
9 |             x: other.x as T,
  |                ^^^^^^^^^^^^
  |
  = note: an `as` expression can only be used to convert between primitive types. Consider using the `From` trait

Looking at this answer I learnt that the From trait doesn't work for i32 to f32 conversion, which is what I wanted originally.

The simplest solution I can come up with is to simply write a function like:

pub fn float2_from_int2(v: Point<i32>) -> Point<f32> {
   Point::<f32>::new(v.x as f32, v.y as f32)
}

Clearly rust has no problem casting from i32 to f32. Is there a nicer way to write this?

回答1:

you can use ToPrimitive trait from num
example (you can avoid Option with AsPrimitive):

pub struct Point<T> {
    pub x: T,
    pub y: T,
}

impl<T: Copy + 'static> Point<T> {
    pub fn from<U: num::cast::AsPrimitive<T>>(other: Point<U>) -> Point<T> {
        Point {
            x: other.x.as_(),
            y: other.y.as_(),
        }
    }
}

fn do_stuff() {
    let a = Point{x: 0i32, y: 0i32};
    let b = Point::<f32>::from(a);
}