整数类型的 Rust 特征边界

Question

Suppose I have my own type as a tuple struct

struct MyType(u8);

And would like to implement the From trait for the other integral types in a generic way, like

impl From<T> for MyType {
    fn from(num: T) -> Self {
        MyType((num & 0xff) as u8)
    }
}

Rust does not allow this because generic types T do not have the as operator. How can I constrain T to the integral types so that as can be used? something along the lines of

impl From<T: Integral> for MyType {...}

Answer 1

You can use the num-traits crate.

PrimInt is the relevant trait, which extends NumCast which allows conversion between the primitive numeric types.

EDIT: Here's an example implementation. It's a bit ugly because many of the relevant conversions return Option , since they don't know ahead of time that the values are in range.

impl<T: PrimInt> From<T> for MyType {
    fn from(num: T) -> Self {
        let clamped = num & T::from(0xFFu8).unwrap();
        Self(clamped.to_u8().unwrap())
    }
}