checked_math.rs

struct Checked<T>(T);

impl<T: CheckedAdd> Add<Checked<T>, Option<Checked<T>>> for Checked<T> {
    fn add(&self, other: &Checked<T>) -> Option<Checked<T>> {
        let (&Checked(ref x), &Checked(ref y)) = (self, other);
        x.checked_add(y).map(|z| Checked(z))
    }
}

impl<T: CheckedSub> Sub<Checked<T>, Option<Checked<T>>> for Checked<T> {
    fn sub(&self, other: &Checked<T>) -> Option<Checked<T>> {
        let (&Checked(ref x), &Checked(ref y)) = (self, other);
        x.checked_sub(y).map(|z| Checked(z))
    }
}

impl<T: CheckedMul> Mul<Checked<T>, Option<Checked<T>>> for Checked<T> {
    fn mul(&self, other: &Checked<T>) -> Option<Checked<T>> {
        let (&Checked(ref x), &Checked(ref y)) = (self, other);
        x.checked_mul(y).map(|z| Checked(z))
    }
}

impl<T: CheckedDiv> Div<Checked<T>, Option<Checked<T>>> for Checked<T> {
    fn div(&self, other: &Checked<T>) -> Option<Checked<T>> {
        let (&Checked(ref x), &Checked(ref y)) = (self, other);
        x.checked_div(y).map(|z| Checked(z))
    }
}

unchecked_math.rs

struct I8(i8);

impl Add<I8, I8> for I8 {
    fn add(&self, other: &I8) -> I8 {
        let (&I8(ref x), &I8(ref y)) = (self, other);
        I8(x.checked_add(y).unwrap())
    }
}

struct UnChecked<T>(T);

impl Add<UnChecked<I8>, UnChecked<I8>> for UnChecked<I8> {
    fn add(&self, other: &UnChecked<I8>) -> UnChecked<I8> {
        match (self, other) {
            (&UnChecked(I8(x)), &UnChecked(I8(y))) => {
                UnChecked(I8(x + y))
            }
        }
    }
}