Numeric types should satisfy the Add trait

[bstrie]

Right now if you write a generic implementation on all types that implement Add, like so:

impl<T: Copy Add<T,T>> Option<T> : Add<Option<T>, Option<T>> {

...attempting to use the implementation on numeric types fails because they haven't technically implemented Add. There should probably be some compiler magic to ensure that numeric types satisfy such generic bounds, even if they don't technically implement the trait.

[graydon]

Considering this impl shows up in libstd now:

impl<T: Copy + Add<T,T>> Add<Option<T>, Option<T>> for Option<T> {
    #[inline(always)]
    fn add(&self, other: &Option<T>) -> Option<T> {
        match (*self, *other) {
            (None, None) => None,
            (_, None) => *self,
            (None, _) => *other,
            (Some(ref lhs), Some(ref rhs)) => Some(*lhs + *rhs)
        }
    }
}

and that this program:

fn main () {
    println(fmt!("%?", Some(1) + Some(2)))
}

prints Some(3), I think this bug is now closed.