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Rollup merge of rust-lang#120936 - ripytide:master, r=Amanieu
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improve `btree_cursors` functions documentation

As suggested by ``@Amanieu`` (and others) in rust-lang#107540 (rust-lang#107540 (comment))

Improvements:
- Document exact behavior of `{upper/lower}_bound{,_mut}` with each of the three `Bound` types using unambigous words `{greatest,greater,smallest,smaller,before,after}`.
- Added another doc-example for the `Bound::Unbounded` for each of the methods
- Changed doc-example to use From<[T; N]> rather than lots of `insert()`s which requires a mutable map which clutters the example when `mut` may not be required for the method (such as for `{upper,lower}_bound`.
- Removed `# Panics` section from `insert_{before,after}` methods since they were changed to return an error instead a while ago.
- Reworded some phrases to be more consistent with the more regular `BTreeMap` methods such as calling entries "key-value" rather than "element"s.
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@matthiaskrgr
matthiaskrgr committed Feb 12, 2024
2 parents 3f67169 + f34d9da commit 8305686
Showing 1 changed file with 128 additions and 85 deletions.
213 changes: 128 additions & 85 deletions library/alloc/src/collections/btree/map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2522,10 +2522,17 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
self.len() == 0
}

/// Returns a [`Cursor`] pointing to the first gap above the given bound.
/// Returns a [`Cursor`] pointing at the gap before the smallest key
/// greater than the given bound.
///
/// Passing [`Bound::Unbounded`] will return a cursor pointing to the start
/// of the map.
/// Passing `Bound::Included(x)` will return a cursor pointing to the
/// gap before the smallest key greater than or equal to `x`.
///
/// Passing `Bound::Excluded(x)` will return a cursor pointing to the
/// gap before the smallest key greater than `x`.
///
/// Passing `Bound::Unbounded` will return a cursor pointing to the
/// gap before the smallest key in the map.
///
/// # Examples
///
Expand All @@ -2535,17 +2542,24 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
/// use std::collections::BTreeMap;
/// use std::ops::Bound;
///
/// let mut a = BTreeMap::new();
/// a.insert(1, "a");
/// a.insert(2, "b");
/// a.insert(3, "c");
/// a.insert(4, "d");
/// let cursor = a.lower_bound(Bound::Included(&2));
/// let map = BTreeMap::from([
/// (1, "a"),
/// (2, "b"),
/// (3, "c"),
/// (4, "d"),
/// ]);
///
/// let cursor = map.lower_bound(Bound::Included(&2));
/// assert_eq!(cursor.peek_prev(), Some((&1, &"a")));
/// assert_eq!(cursor.peek_next(), Some((&2, &"b")));
/// let cursor = a.lower_bound(Bound::Excluded(&2));
///
/// let cursor = map.lower_bound(Bound::Excluded(&2));
/// assert_eq!(cursor.peek_prev(), Some((&2, &"b")));
/// assert_eq!(cursor.peek_next(), Some((&3, &"c")));
///
/// let cursor = map.lower_bound(Bound::Unbounded);
/// assert_eq!(cursor.peek_prev(), None);
/// assert_eq!(cursor.peek_next(), Some((&1, &"a")));
/// ```
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn lower_bound<Q: ?Sized>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>
Expand All @@ -2561,11 +2575,17 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
Cursor { current: Some(edge), root: self.root.as_ref() }
}

/// Returns a [`CursorMut`] pointing to the first gap above the given bound.
/// Returns a [`CursorMut`] pointing at the gap before the smallest key
/// greater than the given bound.
///
/// Passing `Bound::Included(x)` will return a cursor pointing to the
/// gap before the smallest key greater than or equal to `x`.
///
/// Passing [`Bound::Unbounded`] will return a cursor pointing to the start
/// of the map.
/// Passing `Bound::Excluded(x)` will return a cursor pointing to the
/// gap before the smallest key greater than `x`.
///
/// Passing `Bound::Unbounded` will return a cursor pointing to the
/// gap before the smallest key in the map.
///
/// # Examples
///
Expand All @@ -2575,17 +2595,24 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
/// use std::collections::BTreeMap;
/// use std::ops::Bound;
///
/// let mut a = BTreeMap::new();
/// a.insert(1, "a");
/// a.insert(2, "b");
/// a.insert(3, "c");
/// a.insert(4, "d");
/// let mut cursor = a.lower_bound_mut(Bound::Included(&2));
/// let mut map = BTreeMap::from([
/// (1, "a"),
/// (2, "b"),
/// (3, "c"),
/// (4, "d"),
/// ]);
///
/// let mut cursor = map.lower_bound_mut(Bound::Included(&2));
/// assert_eq!(cursor.peek_prev(), Some((&1, &mut "a")));
/// assert_eq!(cursor.peek_next(), Some((&2, &mut "b")));
/// let mut cursor = a.lower_bound_mut(Bound::Excluded(&2));
///
/// let mut cursor = map.lower_bound_mut(Bound::Excluded(&2));
/// assert_eq!(cursor.peek_prev(), Some((&2, &mut "b")));
/// assert_eq!(cursor.peek_next(), Some((&3, &mut "c")));
///
/// let mut cursor = map.lower_bound_mut(Bound::Unbounded);
/// assert_eq!(cursor.peek_prev(), None);
/// assert_eq!(cursor.peek_next(), Some((&1, &mut "a")));
/// ```
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn lower_bound_mut<Q: ?Sized>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A>
Expand Down Expand Up @@ -2618,10 +2645,17 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
}
}

/// Returns a [`Cursor`] pointing at the last gap below the given bound.
/// Returns a [`Cursor`] pointing at the gap after the greatest key
/// smaller than the given bound.
///
/// Passing [`Bound::Unbounded`] will return a cursor pointing to the end
/// of the map.
/// Passing `Bound::Included(x)` will return a cursor pointing to the
/// gap after the greatest key smaller than or equal to `x`.
///
/// Passing `Bound::Excluded(x)` will return a cursor pointing to the
/// gap after the greatest key smaller than `x`.
///
/// Passing `Bound::Unbounded` will return a cursor pointing to the
/// gap after the greatest key in the map.
///
/// # Examples
///
Expand All @@ -2631,17 +2665,24 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
/// use std::collections::BTreeMap;
/// use std::ops::Bound;
///
/// let mut a = BTreeMap::new();
/// a.insert(1, "a");
/// a.insert(2, "b");
/// a.insert(3, "c");
/// a.insert(4, "d");
/// let cursor = a.upper_bound(Bound::Included(&3));
/// let map = BTreeMap::from([
/// (1, "a"),
/// (2, "b"),
/// (3, "c"),
/// (4, "d"),
/// ]);
///
/// let cursor = map.upper_bound(Bound::Included(&3));
/// assert_eq!(cursor.peek_prev(), Some((&3, &"c")));
/// assert_eq!(cursor.peek_next(), Some((&4, &"d")));
/// let cursor = a.upper_bound(Bound::Excluded(&3));
///
/// let cursor = map.upper_bound(Bound::Excluded(&3));
/// assert_eq!(cursor.peek_prev(), Some((&2, &"b")));
/// assert_eq!(cursor.peek_next(), Some((&3, &"c")));
///
/// let cursor = map.upper_bound(Bound::Unbounded);
/// assert_eq!(cursor.peek_prev(), Some((&4, &"d")));
/// assert_eq!(cursor.peek_next(), None);
/// ```
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn upper_bound<Q: ?Sized>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>
Expand All @@ -2657,10 +2698,17 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
Cursor { current: Some(edge), root: self.root.as_ref() }
}

/// Returns a [`CursorMut`] pointing at the last gap below the given bound.
/// Returns a [`CursorMut`] pointing at the gap after the greatest key
/// smaller than the given bound.
///
/// Passing [`Bound::Unbounded`] will return a cursor pointing to the end
/// of the map.
/// Passing `Bound::Included(x)` will return a cursor pointing to the
/// gap after the greatest key smaller than or equal to `x`.
///
/// Passing `Bound::Excluded(x)` will return a cursor pointing to the
/// gap after the greatest key smaller than `x`.
///
/// Passing `Bound::Unbounded` will return a cursor pointing to the
/// gap after the greatest key in the map.
///
/// # Examples
///
Expand All @@ -2670,17 +2718,24 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
/// use std::collections::BTreeMap;
/// use std::ops::Bound;
///
/// let mut a = BTreeMap::new();
/// a.insert(1, "a");
/// a.insert(2, "b");
/// a.insert(3, "c");
/// a.insert(4, "d");
/// let mut cursor = a.upper_bound_mut(Bound::Included(&3));
/// let mut map = BTreeMap::from([
/// (1, "a"),
/// (2, "b"),
/// (3, "c"),
/// (4, "d"),
/// ]);
///
/// let mut cursor = map.upper_bound_mut(Bound::Included(&3));
/// assert_eq!(cursor.peek_prev(), Some((&3, &mut "c")));
/// assert_eq!(cursor.peek_next(), Some((&4, &mut "d")));
/// let mut cursor = a.upper_bound_mut(Bound::Excluded(&3));
///
/// let mut cursor = map.upper_bound_mut(Bound::Excluded(&3));
/// assert_eq!(cursor.peek_prev(), Some((&2, &mut "b")));
/// assert_eq!(cursor.peek_next(), Some((&3, &mut "c")));
///
/// let mut cursor = map.upper_bound_mut(Bound::Unbounded);
/// assert_eq!(cursor.peek_prev(), Some((&4, &mut "d")));
/// assert_eq!(cursor.peek_next(), None);
/// ```
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn upper_bound_mut<Q: ?Sized>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A>
Expand Down Expand Up @@ -3040,8 +3095,8 @@ impl<'a, K, V, A> CursorMutKey<'a, K, V, A> {

// Now the tree editing operations
impl<'a, K: Ord, V, A: Allocator + Clone> CursorMutKey<'a, K, V, A> {
/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMutKey` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap before the
/// newly inserted element.
Expand Down Expand Up @@ -3083,8 +3138,8 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMutKey<'a, K, V, A> {
*self.length += 1;
}

/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMutKey` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap after the
/// newly inserted element.
Expand Down Expand Up @@ -3129,19 +3184,16 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMutKey<'a, K, V, A> {
*self.length += 1;
}

/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMutKey` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap before the
/// newly inserted element.
///
/// # Panics
///
/// This function panics if:
/// - the given key compares less than or equal to the current element (if
/// any).
/// - the given key compares greater than or equal to the next element (if
/// any).
/// If the inserted key is not greater than the key before the cursor
/// (if any), or if it not less than the key after the cursor (if any),
/// then an [`UnorderedKeyError`] is returned since this would
/// invalidate the [`Ord`] invariant between the keys of the map.
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn insert_after(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError> {
if let Some((prev, _)) = self.peek_prev() {
Expand All @@ -3160,19 +3212,16 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMutKey<'a, K, V, A> {
Ok(())
}

/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMutKey` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap after the
/// newly inserted element.
///
/// # Panics
///
/// This function panics if:
/// - the given key compares greater than or equal to the current element
/// (if any).
/// - the given key compares less than or equal to the previous element (if
/// any).
/// If the inserted key is not greater than the key before the cursor
/// (if any), or if it not less than the key after the cursor (if any),
/// then an [`UnorderedKeyError`] is returned since this would
/// invalidate the [`Ord`] invariant between the keys of the map.
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn insert_before(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError> {
if let Some((prev, _)) = self.peek_prev() {
Expand Down Expand Up @@ -3239,10 +3288,10 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMutKey<'a, K, V, A> {
}

impl<'a, K: Ord, V, A: Allocator + Clone> CursorMut<'a, K, V, A> {
/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMut` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap before the
/// After the insertion the cursor will be pointing at the gap after the
/// newly inserted element.
///
/// # Safety
Expand All @@ -3257,8 +3306,8 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMut<'a, K, V, A> {
unsafe { self.inner.insert_after_unchecked(key, value) }
}

/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMut` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap after the
/// newly inserted element.
Expand All @@ -3275,37 +3324,31 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMut<'a, K, V, A> {
unsafe { self.inner.insert_before_unchecked(key, value) }
}

/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMut` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap before the
/// newly inserted element.
///
/// # Panics
///
/// This function panics if:
/// - the given key compares less than or equal to the current element (if
/// any).
/// - the given key compares greater than or equal to the next element (if
/// any).
/// If the inserted key is not greater than the key before the cursor
/// (if any), or if it not less than the key after the cursor (if any),
/// then an [`UnorderedKeyError`] is returned since this would
/// invalidate the [`Ord`] invariant between the keys of the map.
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn insert_after(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError> {
self.inner.insert_after(key, value)
}

/// Inserts a new element into the `BTreeMap` in the gap that the
/// `CursorMut` is currently pointing to.
/// Inserts a new key-value pair into the map in the gap that the
/// cursor is currently pointing to.
///
/// After the insertion the cursor will be pointing at the gap after the
/// newly inserted element.
///
/// # Panics
///
/// This function panics if:
/// - the given key compares greater than or equal to the current element
/// (if any).
/// - the given key compares less than or equal to the previous element (if
/// any).
/// If the inserted key is not greater than the key before the cursor
/// (if any), or if it not less than the key after the cursor (if any),
/// then an [`UnorderedKeyError`] is returned since this would
/// invalidate the [`Ord`] invariant between the keys of the map.
#[unstable(feature = "btree_cursors", issue = "107540")]
pub fn insert_before(&mut self, key: K, value: V) -> Result<(), UnorderedKeyError> {
self.inner.insert_before(key, value)
Expand Down

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