如何实现泛型类型的特征？

Question

In Rust what is the proper way of implementing traits for a generic type? I'm expecting my Vector to consist of integers or floats. Irregardless of the type I want get_magnitude() to output f64. How do I get powi() and sqrt() to work? Any workarounds? I'm stuck

pub struct Vector<T> {
    i: T,
    j: T,
    k: T,
}

impl<T> Vector<T> {
    fn new(i: T, j: T, k: T) -> Vector<T> {
        Vector {
            i,
            j,
            k,
        }
    }
}

impl<T> Vector<T> {
    fn get_magnitude(&self) -> f64 {
        (self.i.powi(2) + self.j.powi(2) + self.k.powi(2)).sqrt()
    }
}

[https://www.codewars.com/kata/58ee4962dc4f81d6f400001c/rust][1]

Answer 1

You can have get_magnitide() constrained to only work when T is applicable. And instead of constraining that T has a powi() , I'd recommend just converting them to f64 initially and doing the math from there.

You can use the AsPrimitive<f64> trait from the num crate for that:

use num::cast::AsPrimitive; // 0.4.0

pub struct Vector<T> {
    i: T,
    j: T,
    k: T,
}

impl<T> Vector<T> {
    fn new(i: T, j: T, k: T) -> Vector<T> {
        Vector { i, j, k }
    }
}

impl<T> Vector<T> {
    fn get_magnitude(&self) -> f64
    where
        T: AsPrimitive<f64>,
    {
        (self.i.as_().powi(2) + self.j.as_().powi(2) + self.k.as_().powi(2)).sqrt()
    }
}

You may also constrain the whole Vector struct to only work when T is a number via the Num trait:

use num::Num; // 0.4.0

pub struct Vector<T>
where
    T: Num
{
    i: T,
    j: T,
    k: T,
}

But you will still need the constraint on get_magnitude() since you're enforcing that it returns a f64 .