comma-ok for pointer-to-union-value

[JoshuaManton]

Currently when pulling out a union value you can do:

val := u.(int);
val, ok := u.(int);

but for pointers you can only do:

val := &u.(int);

which results in a lot of code that looks like this:

if _, ok := u.(int) {
    val := &u.(int);
}

It would be nice if we could do:

val, ok := &u.(int);

I believe the same is true for getting map pointers as well but I am not certain.