use std::ops::{Add, AddAssign, Sub}; #[derive(Copy, Clone, Debug, Default, Eq, PartialEq, Ord, PartialOrd)]pub struct OffsetUtf16(pub usize); impl<'a> Add<&'a Self> for OffsetUtf16 {    type Output = Self;     fn add(self, other: &'a Self) -> Self::Output {        Self(self.0 + other.0)    }} impl Add for OffsetUtf16 {    type Output = Self;     fn add(self, other: Self) -> Self::Output {        Self(self.0 + other.0)    }} impl<'a> Sub<&'a Self> for OffsetUtf16 {    type Output = Self;     fn sub(self, other: &'a Self) -> Self::Output {        debug_assert!(*other <= self);        Self(self.0 - other.0)    }} impl Sub for OffsetUtf16 {    type Output = OffsetUtf16;     fn sub(self, other: Self) -> Self::Output {        Self(self.0 - other.0)    }} impl<'a> AddAssign<&'a Self> for OffsetUtf16 {    fn add_assign(&mut self, other: &'a Self) {        self.0 += other.0;    }} impl AddAssign<Self> for OffsetUtf16 {    fn add_assign(&mut self, other: Self) {        self.0 += other.0;    }}