Trait ref_ops::RefNeg

source · [−]
pub trait RefNeg: Neg {
    fn ref_neg(&self) -> Self::Output;
}
Expand description

An escape hatch for implimenting Neg for references to newtypes.

As of Rust 1.52.1, the following code does not compile:

ⓘ
use core::ops::Neg;

#[derive(PartialEq)]
struct A<T>(T);

impl<'a, T> Neg for &'a A<T>
where
    T: Neg,
    &'a T: Neg<Output = T::Output>,
{
    type Output = A<T::Output>;

    fn neg(self) -> Self::Output {
        A(self.0.neg())
    }
}

fn f<T>(a: T)
where
    for<'a> &'a T: Neg,
{
    let neg_a = (&a).neg();

    // to do something with `a` and `neg_a`
    todo!();
}

fn g<T>(a: T)
where
    for<'a> &'a T: Neg,
{
    f(a);
}

assert!(-&A(1.0) == A(-1.0));

but the following code does:

use core::ops::Neg;
use ref_ops::RefNeg;

#[derive(PartialEq)]
struct A<T>(T);

impl<T> Neg for &A<T>
where
    T: RefNeg,
{
    type Output = A<T::Output>;

    fn neg(self) -> Self::Output {
        A(self.0.ref_neg())
    }
}

fn f<T>(a: T)
where
    for<'a> &'a T: Neg,
{
    let neg_a = (&a).neg();

    // to do something with `a` and `neg_a`
    todo!();
}

fn g<T>(a: T)
where
    for<'a> &'a T: Neg,
{
    f(a);
}

assert!(-&A(1.0) == A(-1.0));

Required Methods

Implementors