abstracting over fields with trait abuses: reddit.com/r/rust/comments/bc2w4m/announcing_rust_1340/eks8tq5/?context=3

playground.rs

trait Field {
    type ValueType;
}

use std::marker::PhantomData as Marker;

struct X<T>(Marker<T>);
struct Y<T>(Marker<T>);
struct Z<T>(Marker<T>);

impl<T> Field for X<T> {
    type ValueType = T;
}

impl<T> Field for Y<T> {
    type ValueType = T;
}

impl<T> Field for Z<T> {
    type ValueType = T;
}

trait HasField<F: Field> {
    fn field(&self) -> &F::ValueType;
    fn field_mut(&mut self) -> &mut F::ValueType;
}

#[derive(Debug, Default)]
struct Vec3<T>(T, T, T);

impl<T> HasField<X<T>> for Vec3<T> {
    fn field(&self) -> &<X<T> as Field>::ValueType { &self.0 }
    fn field_mut(&mut self) -> &mut <X<T> as Field>::ValueType { &mut self.0 }
}

impl<T> HasField<Y<T>> for Vec3<T> {
    fn field(&self) -> &<Y<T> as Field>::ValueType { &self.1 }
    fn field_mut(&mut self) -> &mut <Y<T> as Field>::ValueType { &mut self.1 }
}

impl<T> HasField<Z<T>> for Vec3<T> {
    fn field(&self) -> &<Z<T> as Field>::ValueType { &self.2 }
    fn field_mut(&mut self) -> &mut <Z<T> as Field>::ValueType { &mut self.2 }
}

fn main() {
    let mut vec = Vec3::<u32>::default();
    *HasField::<X<_>>::field_mut(&mut vec) = 1;
    *HasField::<Y<_>>::field_mut(&mut vec) = 2;
    *HasField::<Z<_>>::field_mut(&mut vec) = 3;
    println!("{:?}", vec);
}