vector_map/

set.rs

use alloc::vec::Vec;

use crate::{Keys, VecMap};
use core::{
    fmt,
    iter::{Chain, FromIterator},
    ops::{BitAnd, BitOr, BitXor, Sub},
};

#[derive(Clone)]
pub struct VecSet<T> {
    map: VecMap<T, ()>,
}

impl<T: PartialEq> VecSet<T> {
    /// Creates an empty VecSet.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let mut set: VecSet<i32> = VecSet::new();
    /// ```
    #[inline]
    pub fn new() -> VecSet<T> {
        VecSet { map: VecMap::new() }
    }

    /// Creates an empty VecSet with space for at least `n` elements in
    /// the map.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let mut set: VecSet<i32> = VecSet::with_capacity(10);
    /// ```
    #[inline]
    pub fn with_capacity(capacity: usize) -> VecSet<T> {
        VecSet {
            map: VecMap::with_capacity(capacity),
        }
    }
}

impl<T> VecSet<T> {
    /// Returns the number of elements the set can hold without reallocating.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let set: VecSet<i32> = VecSet::with_capacity(100);
    /// assert!(set.capacity() >= 100);
    /// ```
    #[inline]
    pub fn capacity(&self) -> usize {
        self.map.capacity()
    }

    /// Reserves capacity for at least `additional` more elements to be inserted
    /// in the `VecSet`. The collection may reserve more space to avoid
    /// frequent reallocations.
    ///
    /// # Panics
    ///
    /// Panics if the new allocation size overflows `usize`.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let mut set: VecSet<i32> = VecSet::new();
    /// set.reserve(10);
    /// ```
    pub fn reserve(&mut self, additional: usize) {
        self.map.reserve(additional)
    }

    /// Shrinks the capacity of the set as much as possible. It will drop
    /// down as much as possible while maintaining the internal rules
    /// and possibly leaving some space in accordance with the resize policy.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let mut set = VecSet::with_capacity(100);
    /// set.insert(1);
    /// set.insert(2);
    /// assert!(set.capacity() >= 100);
    /// set.shrink_to_fit();
    /// assert!(set.capacity() >= 2);
    /// ```
    pub fn shrink_to_fit(&mut self) {
        self.map.shrink_to_fit()
    }

    /// An iterator visiting all elements in arbitrary order.
    /// Iterator element type is &'a T.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let mut set = VecSet::new();
    /// set.insert("a");
    /// set.insert("b");
    ///
    /// // Will print in an arbitrary order.
    /// for x in set.iter() {
    ///     println!("{}", x);
    /// }
    /// ```
    pub fn iter(&self) -> Iter<'_, T> {
        Iter {
            iter: self.map.keys(),
        }
    }

    /// Visit the values representing the difference.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let a: VecSet<_> = [1, 2, 3].iter().cloned().collect();
    /// let b: VecSet<_> = [4, 2, 3, 4].iter().cloned().collect();
    ///
    /// // Can be seen as `a - b`.
    /// for x in a.difference(&b) {
    ///     println!("{}", x); // Print 1
    /// }
    ///
    /// let diff: VecSet<_> = a.difference(&b).cloned().collect();
    /// assert_eq!(diff, [1].iter().cloned().collect());
    ///
    /// // Note that difference is not symmetric,
    /// // and `b - a` means something else:
    /// let diff: VecSet<_> = b.difference(&a).cloned().collect();
    /// assert_eq!(diff, [4].iter().cloned().collect());
    /// ```
    pub fn difference<'a>(&'a self, other: &'a VecSet<T>) -> Difference<'a, T>
    where
        T: PartialEq,
    {
        Difference {
            iter: self.iter(),
            other,
        }
    }

    /// Visit the values representing the symmetric difference.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let a: VecSet<_> = [1, 2, 3].iter().cloned().collect();
    /// let b: VecSet<_> = [4, 2, 3, 4].iter().cloned().collect();
    ///
    /// // Print 1, 4 in arbitrary order.
    /// for x in a.symmetric_difference(&b) {
    ///     println!("{}", x);
    /// }
    ///
    /// let diff1: VecSet<_> = a.symmetric_difference(&b).cloned().collect();
    /// let diff2: VecSet<_> = b.symmetric_difference(&a).cloned().collect();
    ///
    /// assert_eq!(diff1, diff2);
    /// assert_eq!(diff1, [1, 4].iter().cloned().collect());
    /// ```
    pub fn symmetric_difference<'a>(&'a self, other: &'a VecSet<T>) -> SymmetricDifference<'a, T>
    where
        T: PartialEq,
    {
        SymmetricDifference {
            iter: self.difference(other).chain(other.difference(self)),
        }
    }

    /// Visit the values representing the intersection.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let a: VecSet<_> = [1, 2, 3].iter().cloned().collect();
    /// let b: VecSet<_> = [4, 2, 3, 4].iter().cloned().collect();
    ///
    /// // Print 2, 3 in arbitrary order.
    /// for x in a.intersection(&b) {
    ///     println!("{}", x);
    /// }
    ///
    /// let intersection: VecSet<_> = a.intersection(&b).cloned().collect();
    /// assert_eq!(intersection, [2, 3].iter().cloned().collect());
    /// ```
    pub fn intersection<'a>(&'a self, other: &'a VecSet<T>) -> Intersection<'a, T> {
        Intersection {
            iter: self.iter(),
            other,
        }
    }

    /// Visit the values representing the union.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let a: VecSet<_> = [1, 2, 3].iter().cloned().collect();
    /// let b: VecSet<_> = [4, 2, 3, 4].iter().cloned().collect();
    ///
    /// // Print 1, 2, 3, 4 in arbitrary order.
    /// for x in a.union(&b) {
    ///     println!("{}", x);
    /// }
    ///
    /// let union: VecSet<_> = a.union(&b).cloned().collect();
    /// assert_eq!(union, [1, 2, 3, 4].iter().cloned().collect());
    /// ```
    pub fn union<'a>(&'a self, other: &'a VecSet<T>) -> Union<'a, T>
    where
        T: PartialEq,
    {
        Union {
            iter: self.iter().chain(other.difference(self)),
        }
    }

    /// Returns the number of elements in the set.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let mut v = VecSet::new();
    /// assert_eq!(v.len(), 0);
    /// v.insert(1);
    /// assert_eq!(v.len(), 1);
    /// ```
    pub fn len(&self) -> usize {
        self.map.len()
    }

    /// Returns true if the set contains no elements.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let mut v = VecSet::new();
    /// assert!(v.is_empty());
    /// v.insert(1);
    /// assert!(!v.is_empty());
    /// ```
    pub fn is_empty(&self) -> bool {
        self.map.is_empty()
    }

    /// Clears the set, returning all elements in an iterator.
    #[inline]
    pub fn drain(&mut self) -> Drain<'_, T> {
        Drain {
            iter: self.map.drain(),
        }
    }

    /// Clears the set, removing all values.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let mut v = VecSet::new();
    /// v.insert(1);
    /// v.clear();
    /// assert!(v.is_empty());
    /// ```
    pub fn clear(&mut self) {
        self.map.clear()
    }

    /// Retains only the elements specified by the predicate.
    ///
    /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
    ///
    pub fn retain<F>(&mut self, mut f: F)
    where
        F: FnMut(&T) -> bool,
    {
        self.map.retain(|k, _| f(k));
    }

    /// Returns `true` if the set contains a value.
    ///
    /// The value may be any borrowed form of the set's value type, but
    /// `Eq` on the borrowed form *must* match those for
    /// the value type.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let set: VecSet<_> = [1, 2, 3].iter().cloned().collect();
    /// assert_eq!(set.contains(&1), true);
    /// assert_eq!(set.contains(&4), false);
    /// ```
    pub fn contains<Q: PartialEq<T> + ?Sized>(&self, value: &Q) -> bool {
        self.map.contains_key(value)
    }

    /// Returns `true` if the set has no elements in common with `other`.
    /// This is equivalent to checking for an empty intersection.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let a: VecSet<_> = [1, 2, 3].iter().cloned().collect();
    /// let mut b = VecSet::new();
    ///
    /// assert_eq!(a.is_disjoint(&b), true);
    /// b.insert(4);
    /// assert_eq!(a.is_disjoint(&b), true);
    /// b.insert(1);
    /// assert_eq!(a.is_disjoint(&b), false);
    /// ```
    pub fn is_disjoint(&self, other: &VecSet<T>) -> bool
    where
        T: PartialEq,
    {
        self.iter().all(|v| !other.contains(v))
    }

    /// Returns `true` if the set is a subset of another.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let sup: VecSet<_> = [1, 2, 3].iter().cloned().collect();
    /// let mut set = VecSet::new();
    ///
    /// assert_eq!(set.is_subset(&sup), true);
    /// set.insert(2);
    /// assert_eq!(set.is_subset(&sup), true);
    /// set.insert(4);
    /// assert_eq!(set.is_subset(&sup), false);
    /// ```
    pub fn is_subset(&self, other: &VecSet<T>) -> bool
    where
        T: PartialEq,
    {
        self.iter().all(|v| other.contains(v))
    }

    /// Returns `true` if the set is a superset of another.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let sub: VecSet<_> = [1, 2].iter().cloned().collect();
    /// let mut set = VecSet::new();
    ///
    /// assert_eq!(set.is_superset(&sub), false);
    ///
    /// set.insert(0);
    /// set.insert(1);
    /// assert_eq!(set.is_superset(&sub), false);
    ///
    /// set.insert(2);
    /// assert_eq!(set.is_superset(&sub), true);
    /// ```
    #[inline]
    pub fn is_superset(&self, other: &VecSet<T>) -> bool
    where
        T: PartialEq,
    {
        other.is_subset(self)
    }

    /// Adds a value to the set.
    ///
    /// If the set did not have a value present, `true` is returned.
    ///
    /// If the set did have this key present, `false` is returned.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let mut set = VecSet::new();
    ///
    /// assert_eq!(set.insert(2), true);
    /// assert_eq!(set.insert(2), false);
    /// assert_eq!(set.len(), 1);
    /// ```
    pub fn insert(&mut self, value: T) -> bool
    where
        T: PartialEq,
    {
        self.map.insert(value, ()).is_none()
    }

    /// Removes a value from the set. Returns `true` if the value was
    /// present in the set.
    ///
    /// The value may be any borrowed form of the set's value type, but
    /// `Eq` on the borrowed form *must* match those for
    /// the value type.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let mut set = VecSet::new();
    ///
    /// set.insert(2);
    /// assert_eq!(set.remove(&2), true);
    /// assert_eq!(set.remove(&2), false);
    /// ```
    pub fn remove<Q: PartialEq<T> + ?Sized>(&mut self, value: &Q) -> bool {
        self.map.remove(value).is_some()
    }
}

impl<T> PartialEq for VecSet<T>
where
    T: PartialEq,
{
    fn eq(&self, other: &VecSet<T>) -> bool {
        if self.len() != other.len() {
            return false;
        }

        self.iter().all(|key| other.contains(key))
    }
}

impl<T> Eq for VecSet<T> where T: Eq {}

impl<T> fmt::Debug for VecSet<T>
where
    T: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_set().entries(self.iter()).finish()
    }
}

impl<T> FromIterator<T> for VecSet<T>
where
    T: PartialEq,
{
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> VecSet<T> {
        let iterator = iter.into_iter();
        let lower = iterator.size_hint().0;
        let mut set = VecSet::with_capacity(lower);
        set.extend(iterator);
        set
    }
}

impl<T> Extend<T> for VecSet<T>
where
    T: PartialEq,
{
    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
        for k in iter {
            self.insert(k);
        }
    }
}

impl<'a, T> Extend<&'a T> for VecSet<T>
where
    T: 'a + PartialEq + Copy,
{
    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
        self.extend(iter.into_iter().cloned());
    }
}

impl<T> Default for VecSet<T>
where
    T: PartialEq,
{
    fn default() -> VecSet<T> {
        VecSet::new()
    }
}

impl<K: PartialEq> From<VecSet<K>> for Vec<K> {
    fn from(val: VecSet<K>) -> Self {
        val.map.keys
    }
}

impl<T> BitOr<&VecSet<T>> for &VecSet<T>
where
    T: PartialEq + Clone,
{
    type Output = VecSet<T>;

    /// Returns the union of `self` and `rhs` as a new `VecSet<T>`.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let a: VecSet<_> = vec![1, 2, 3].into_iter().collect();
    /// let b: VecSet<_> = vec![3, 4, 5].into_iter().collect();
    ///
    /// let set = &a | &b;
    ///
    /// let mut i = 0;
    /// let expected = [1, 2, 3, 4, 5];
    /// for x in &set {
    ///     assert!(expected.contains(x));
    ///     i += 1;
    /// }
    /// assert_eq!(i, expected.len());
    /// ```
    fn bitor(self, rhs: &VecSet<T>) -> VecSet<T> {
        self.union(rhs).cloned().collect()
    }
}

impl<T> BitAnd<&VecSet<T>> for &VecSet<T>
where
    T: PartialEq + Clone,
{
    type Output = VecSet<T>;

    /// Returns the intersection of `self` and `rhs` as a new `VecSet<T>`.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let a: VecSet<_> = vec![1, 2, 3].into_iter().collect();
    /// let b: VecSet<_> = vec![2, 3, 4].into_iter().collect();
    ///
    /// let set = &a & &b;
    ///
    /// let mut i = 0;
    /// let expected = [2, 3];
    /// for x in &set {
    ///     assert!(expected.contains(x));
    ///     i += 1;
    /// }
    /// assert_eq!(i, expected.len());
    /// ```
    fn bitand(self, rhs: &VecSet<T>) -> VecSet<T> {
        self.intersection(rhs).cloned().collect()
    }
}

impl<T> BitXor<&VecSet<T>> for &VecSet<T>
where
    T: PartialEq + Clone,
{
    type Output = VecSet<T>;

    /// Returns the symmetric difference of `self` and `rhs` as a new `VecSet<T>`.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let a: VecSet<_> = vec![1, 2, 3].into_iter().collect();
    /// let b: VecSet<_> = vec![3, 4, 5].into_iter().collect();
    ///
    /// let set = &a ^ &b;
    ///
    /// let mut i = 0;
    /// let expected = [1, 2, 4, 5];
    /// for x in &set {
    ///     assert!(expected.contains(x));
    ///     i += 1;
    /// }
    /// assert_eq!(i, expected.len());
    /// ```
    fn bitxor(self, rhs: &VecSet<T>) -> VecSet<T> {
        self.symmetric_difference(rhs).cloned().collect()
    }
}

impl<T> Sub<&VecSet<T>> for &VecSet<T>
where
    T: PartialEq + Clone,
{
    type Output = VecSet<T>;

    /// Returns the difference of `self` and `rhs` as a new `VecSet<T>`.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    ///
    /// let a: VecSet<_> = vec![1, 2, 3].into_iter().collect();
    /// let b: VecSet<_> = vec![3, 4, 5].into_iter().collect();
    ///
    /// let set = &a - &b;
    ///
    /// let mut i = 0;
    /// let expected = [1, 2];
    /// for x in &set {
    ///     assert!(expected.contains(x));
    ///     i += 1;
    /// }
    /// assert_eq!(i, expected.len());
    /// ```
    fn sub(self, rhs: &VecSet<T>) -> VecSet<T> {
        self.difference(rhs).cloned().collect()
    }
}

/// VecSet iterator
pub struct Iter<'a, K: 'a> {
    iter: Keys<'a, K, ()>,
}

/// VecSet move iterator
pub struct IntoIter<K> {
    iter: super::IntoIter<K, ()>,
}

/// VecSet drain iterator
pub struct Drain<'a, K: 'a> {
    iter: super::Drain<'a, K, ()>,
}

/// Intersection iterator
pub struct Intersection<'a, T: 'a> {
    // iterator of the first set
    iter: Iter<'a, T>,
    // the second set
    other: &'a VecSet<T>,
}

/// Difference iterator
pub struct Difference<'a, T: 'a>
where
    T: PartialEq,
{
    // iterator of the first set
    iter: Iter<'a, T>,
    // the second set
    other: &'a VecSet<T>,
}

/// Symmetric difference iterator.
pub struct SymmetricDifference<'a, T: 'a>
where
    T: PartialEq,
{
    iter: Chain<Difference<'a, T>, Difference<'a, T>>,
}

/// Set union iterator.
pub struct Union<'a, T: 'a>
where
    T: PartialEq,
{
    iter: Chain<Iter<'a, T>, Difference<'a, T>>,
}

impl<'a, T> IntoIterator for &'a VecSet<T>
where
    T: PartialEq,
{
    type Item = &'a T;
    type IntoIter = Iter<'a, T>;

    fn into_iter(self) -> Iter<'a, T> {
        self.iter()
    }
}

impl<T> IntoIterator for VecSet<T>
where
    T: PartialEq,
{
    type Item = T;
    type IntoIter = IntoIter<T>;

    /// Creates a consuming iterator, that is, one that moves each value out
    /// of the set in arbitrary order. The set cannot be used after calling
    /// this.
    ///
    /// # Examples
    ///
    /// ```
    /// use vector_map::set::VecSet;;
    /// let mut set = VecSet::new();
    /// set.insert("a".to_string());
    /// set.insert("b".to_string());
    ///
    /// // Not possible to collect to a Vec<String> with a regular `.iter()`.
    /// let v: Vec<String> = set.into_iter().collect();
    ///
    /// // Will print in an arbitrary order.
    /// for x in &v {
    ///     println!("{}", x);
    /// }
    /// ```
    fn into_iter(self) -> IntoIter<T> {
        IntoIter {
            iter: self.map.into_iter(),
        }
    }
}

impl<'a, K> Clone for Iter<'a, K> {
    fn clone(&self) -> Iter<'a, K> {
        Iter {
            iter: self.iter.clone(),
        }
    }
}
impl<'a, K> Iterator for Iter<'a, K> {
    type Item = &'a K;

    fn next(&mut self) -> Option<&'a K> {
        self.iter.next()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}
impl<'a, K> ExactSizeIterator for Iter<'a, K> {
    fn len(&self) -> usize {
        self.iter.len()
    }
}

impl<K> Iterator for IntoIter<K> {
    type Item = K;

    fn next(&mut self) -> Option<K> {
        self.iter.next().map(|(k, _)| k)
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}
impl<K> ExactSizeIterator for IntoIter<K> {
    fn len(&self) -> usize {
        self.iter.len()
    }
}

impl<'a, K> Iterator for Drain<'a, K> {
    type Item = K;

    fn next(&mut self) -> Option<K> {
        self.iter.next().map(|(k, _)| k)
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}
impl<'a, K> ExactSizeIterator for Drain<'a, K> {
    fn len(&self) -> usize {
        self.iter.len()
    }
}

impl<'a, T> Clone for Intersection<'a, T> {
    fn clone(&self) -> Intersection<'a, T> {
        Intersection {
            iter: self.iter.clone(),
            ..*self
        }
    }
}

impl<'a, T> Iterator for Intersection<'a, T>
where
    T: PartialEq,
{
    type Item = &'a T;

    fn next(&mut self) -> Option<&'a T> {
        loop {
            match self.iter.next() {
                None => return None,
                Some(elt) => {
                    if self.other.contains(elt) {
                        return Some(elt);
                    }
                }
            }
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, upper) = self.iter.size_hint();
        (0, upper)
    }
}

impl<'a, T> Clone for Difference<'a, T>
where
    T: PartialEq,
{
    fn clone(&self) -> Difference<'a, T> {
        Difference {
            iter: self.iter.clone(),
            ..*self
        }
    }
}

impl<'a, T> Iterator for Difference<'a, T>
where
    T: PartialEq,
{
    type Item = &'a T;

    fn next(&mut self) -> Option<&'a T> {
        loop {
            match self.iter.next() {
                None => return None,
                Some(elt) => {
                    if !self.other.contains(elt) {
                        return Some(elt);
                    }
                }
            }
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, upper) = self.iter.size_hint();
        (0, upper)
    }
}

impl<'a, T> Clone for SymmetricDifference<'a, T>
where
    T: PartialEq,
{
    fn clone(&self) -> SymmetricDifference<'a, T> {
        SymmetricDifference {
            iter: self.iter.clone(),
        }
    }
}

impl<'a, T> Iterator for SymmetricDifference<'a, T>
where
    T: PartialEq,
{
    type Item = &'a T;

    fn next(&mut self) -> Option<&'a T> {
        self.iter.next()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

impl<'a, T> Clone for Union<'a, T>
where
    T: PartialEq,
{
    fn clone(&self) -> Union<'a, T> {
        Union {
            iter: self.iter.clone(),
        }
    }
}

impl<'a, T> Iterator for Union<'a, T>
where
    T: PartialEq,
{
    type Item = &'a T;

    fn next(&mut self) -> Option<&'a T> {
        self.iter.next()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

#[allow(dead_code)]
fn assert_covariance() {
    fn set<'new>(v: VecSet<&'static str>) -> VecSet<&'new str> {
        v
    }
    fn iter<'a, 'new>(v: Iter<'a, &'static str>) -> Iter<'a, &'new str> {
        v
    }
    fn into_iter<'new>(v: IntoIter<&'static str>) -> IntoIter<&'new str> {
        v
    }
    fn difference<'a, 'new>(v: Difference<'a, &'static str>) -> Difference<'a, &'new str> {
        v
    }
    fn symmetric_difference<'a, 'new>(
        v: SymmetricDifference<'a, &'static str>,
    ) -> SymmetricDifference<'a, &'new str> {
        v
    }
    fn intersection<'a, 'new>(v: Intersection<'a, &'static str>) -> Intersection<'a, &'new str> {
        v
    }
    fn union<'a, 'new>(v: Union<'a, &'static str>) -> Union<'a, &'new str> {
        v
    }
}