Making a method generic over Array1

Question

I have the following Trait implementation and would like to make unit generic over Array1<T>, but fail to find the right Trait bounds (especially that this somehow seems trivial to me, all T needs to support is basically basic arithmetic that output T for the function to work).

trait Unit {
    fn unit(&self) -> Array1<f32>;
}

impl Unit for Array1<f32> 
{
    fn unit(&self) -> Array1<f32> {
        self / (self * self).sum().sqrt()
    }
}

The compiler suggests adding std::ops::Mul<Output = &ArrayBase<OwnedRepr<T>, Dim<[usize; 1]>>>, but doing so keeps giving the same error over and over.

PlayGround

@AlexeyRomanov The `unit` method over all Array1. Sorry if it was not clear. — zareami10, Sep 10 '21 at 16:04
But then do you still have `impl Unit for Array1`? What should `let x: Array1 = ...; let y = x.unit::()` actually do and what do you expect the type of `y` to be? — Alexey Romanov, Sep 10 '21 at 16:28
@AlexeyRomanov I want to have `impl Unit for Array1` so I can calculate the unit vector regardless of the type (e.g. f32, f64, u16,...) as long as they are numeric-like without having to manually implement all those by myself. I'm not sure whether this would require changes in the Trait definition itself or not. — zareami10, Sep 10 '21 at 16:49

score 2 · Accepted Answer · answered Sep 10 '21 at 16:50

I followed the compiler error messages and produced this generic code that compiles. I'm not familiar with ndarray so I don't know if this is actually correct.

use std::ops::Mul;
use num_traits::{Zero, real::Real};
use ndarray::prelude::*;

trait Unit {
    type Output;
    fn unit(&self) -> Array1<Self::Output>;
}

impl<T> Unit for Array1<T>
where
    for<'a> &'a Array1<T>: Mul<Output = Array1<T>>,
    T: Real + Clone + Zero + ndarray::ScalarOperand,
{
    type Output = T;
    fn unit(&self) -> Array1<T> {
        self / (self * self).sum().sqrt()
    }
}

Note that Unit now returns an associated type. If you want it to always return f32 then you'll need to require that T can be converted to f32 too.

Making a method generic over Array1

1 Answers1