Implement TreeSet interface

[declanvk]

Like the TreeMap corresponding to BTreeMap, TreeSet should copy BTreeSet where possible.

https://doc.rust-lang.org/stable/std/collections/struct.BTreeSet.html

impl<T> BTreeSet<T> {
    pub const fn new() -> BTreeSet<T>;

    pub fn range<K: ?Sized, R>(&self, range: R) -> Range<'_, T>
    where
        K: Ord,
        T: Borrow<K> + Ord,
        R: RangeBounds<K>;

    pub fn difference<'a>(&'a self, other: &'a BTreeSet<T, A>) -> Difference<'a, T, A>
    where
        T: Ord;

    pub fn symmetric_difference<'a>(
        &'a self,
        other: &'a BTreeSet<T, A>,
    ) -> SymmetricDifference<'a, T>
    where
        T: Ord;

    pub fn intersection<'a>(&'a self, other: &'a BTreeSet<T, A>) -> Intersection<'a, T, A>
    where
        T: Ord;

    pub fn union<'a>(&'a self, other: &'a BTreeSet<T, A>) -> Union<'a, T>
    where
        T: Ord;

    pub fn clear(&mut self)
    where
        A: Clone;

    pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
    where
        T: Borrow<Q> + Ord,
        Q: Ord;

    pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
    where
        T: Borrow<Q> + Ord,
        Q: Ord;

    pub fn is_disjoint(&self, other: &BTreeSet<T, A>) -> bool
    where
        T: Ord;

    pub fn is_subset(&self, other: &BTreeSet<T, A>) -> bool
    where
        T: Ord;

    pub fn is_superset(&self, other: &BTreeSet<T, A>) -> bool
    where
        T: Ord;

    pub fn first(&self) -> Option<&T>
    where
        T: Ord;

    pub fn last(&self) -> Option<&T>
    where
        T: Ord;

    pub fn pop_first(&mut self) -> Option<T>
    where
        T: Ord;

    pub fn pop_last(&mut self) -> Option<T>
    where
        T: Ord;

    pub fn insert(&mut self, value: T) -> bool
    where
        T: Ord;

    pub fn replace(&mut self, value: T) -> Option<T>
    where
        T: Ord;

    pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
    where
        T: Borrow<Q> + Ord,
        Q: Ord;

    pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
    where
        T: Borrow<Q> + Ord,
        Q: Ord;

    pub fn retain<F>(&mut self, mut f: F)
    where
        T: Ord,
        F: FnMut(&T) -> bool;

    pub fn append(&mut self, other: &mut Self)
    where
        T: Ord,
        A: Clone;

    pub fn split_off<Q: ?Sized + Ord>(&mut self, value: &Q) -> Self
    where
        T: Borrow<Q> + Ord,
        A: Clone;

    pub fn drain_filter<'a, F>(&'a mut self, pred: F) -> DrainFilter<'a, T, F, A>
    where
        T: Ord,
        F: 'a + FnMut(&T) -> bool;

    pub fn iter(&self) -> Iter<'_, T>;

    pub const fn len(&self) -> usize;

    pub const fn is_empty(&self) -> bool;
}