pub fn drain_filter<'a, F>(&'a mut self, pred: F) -> DrainFilter<'a, T, F>
    where
        T: Ord,
        F: 'a + FnMut(&T) -> bool,
    {
        DrainFilter { pred, inner: self.map.drain_filter_inner() }
    }
Gets an iterator for moving out the `BTreeSet`'s contents.

# Examples

```
use std::collections::BT
benchmarks/haystacks/code/rust-library.rs