pub fn leave(&self) -> Collection<G, D, R> {
        self.inner
            .leave()
            .map(|(data, time, diff)| (data, time.to_outer(), diff))
            .as_collection()
    }
Returns the final value of a Collection from a nested scope to its containing scope.

# Examples

```
use timely::dataflow::Scope;
use differential_dataflow::input::Input;

::timely::example(|scope| {

let data = scope.new_collection_from(1 .. 10).1;

let result = scope.region(|child| {
data.enter(child)
.leave()
});

data.assert_eq(&result);
});
```
differential-dataflow/src/collection.rs