如何使用 OR 逻辑指定特征边界

Question

I am looking to implement 2D matrix functionality in Rust in a generic fashion where the elements of the matrix would be numerics (either i32, i64, u32, u64, f32, f64). The generic type would look something like shown below:

#[derive(Debug)]
pub struct Mat<T> {
    data: Vec<T>,
    shape: (usize, usize),
}

impl<T> Mat<T> where T: i32 OR i64 OR u32 OR u64 OR f32 OR f64{
    pub fn new(){
        ...
    }
}

I know that you can AND trait bounds with the + symbol in the form of " where T: bound1 + bound2 ". Is there a way to cleanly OR trait bounds together?

Answer 1

No, but this isn't usually what you want anyway. You can do this by declaring a tag trait, like:

pub trait NumberType {}

impl NumberTrait for i32 {}
impl NumberTrait for i64 {}
// and so on...

impl<T> Mat<T> where T: NumberType { ... }

However, usually what you're actually trying to accomplish is enforcing that T supports some set of operations like addition and multiplication. If so, just bound on those operations:

use std::ops::*;

impl<T> Mat<T> where T: Add<T, Output=T> + Mul<T, Output=T> { ... }

This will cover all of the primitive numeric types, but will also cover other types for which those operations are defined, such as third-party "decimal" or "big number" (eg 128/256/512-bit integers) types.