Struct std::collections::BTreeMap

1.0.0 · source ·
pub struct BTreeMap<K, V, A = Global>where
    A: Allocator + Clone,{ /* private fields */ }
Expand description

An ordered map based on a B-Tree.

B-Trees represent a fundamental compromise between cache-efficiency and actually minimizing the amount of work performed in a search. In theory, a binary search tree (BST) is the optimal choice for a sorted map, as a perfectly balanced BST performs the theoretical minimum amount of comparisons necessary to find an element (log2n). However, in practice the way this is done is very inefficient for modern computer architectures. In particular, every element is stored in its own individually heap-allocated node. This means that every single insertion triggers a heap-allocation, and every single comparison should be a cache-miss. Since these are both notably expensive things to do in practice, we are forced to, at the very least, reconsider the BST strategy.

A B-Tree instead makes each node contain B-1 to 2B-1 elements in a contiguous array. By doing this, we reduce the number of allocations by a factor of B, and improve cache efficiency in searches. However, this does mean that searches will have to do more comparisons on average. The precise number of comparisons depends on the node search strategy used. For optimal cache efficiency, one could search the nodes linearly. For optimal comparisons, one could search the node using binary search. As a compromise, one could also perform a linear search that initially only checks every ith element for some choice of i.

Currently, our implementation simply performs naive linear search. This provides excellent performance on small nodes of elements which are cheap to compare. However in the future we would like to further explore choosing the optimal search strategy based on the choice of B, and possibly other factors. Using linear search, searching for a random element is expected to take B * log(n) comparisons, which is generally worse than a BST. In practice, however, performance is excellent.

It is a logic error for a key to be modified in such a way that the key’s ordering relative to any other key, as determined by the Ord trait, changes while it is in the map. This is normally only possible through Cell, RefCell, global state, I/O, or unsafe code. The behavior resulting from such a logic error is not specified, but will be encapsulated to the BTreeMap that observed the logic error and not result in undefined behavior. This could include panics, incorrect results, aborts, memory leaks, and non-termination.

Iterators obtained from functions such as BTreeMap::iter, BTreeMap::values, or BTreeMap::keys produce their items in order by key, and take worst-case logarithmic and amortized constant time per item returned.

Examples

use std::collections::BTreeMap;

// type inference lets us omit an explicit type signature (which
// would be `BTreeMap<&str, &str>` in this example).
let mut movie_reviews = BTreeMap::new();

// review some movies.
movie_reviews.insert("Office Space",       "Deals with real issues in the workplace.");
movie_reviews.insert("Pulp Fiction",       "Masterpiece.");
movie_reviews.insert("The Godfather",      "Very enjoyable.");
movie_reviews.insert("The Blues Brothers", "Eye lyked it a lot.");

// check for a specific one.
if !movie_reviews.contains_key("Les Misérables") {
    println!("We've got {} reviews, but Les Misérables ain't one.",
             movie_reviews.len());
}

// oops, this review has a lot of spelling mistakes, let's delete it.
movie_reviews.remove("The Blues Brothers");

// look up the values associated with some keys.
let to_find = ["Up!", "Office Space"];
for movie in &to_find {
    match movie_reviews.get(movie) {
       Some(review) => println!("{movie}: {review}"),
       None => println!("{movie} is unreviewed.")
    }
}

// Look up the value for a key (will panic if the key is not found).
println!("Movie review: {}", movie_reviews["Office Space"]);

// iterate over everything.
for (movie, review) in &movie_reviews {
    println!("{movie}: \"{review}\"");
}
Run

A BTreeMap with a known list of items can be initialized from an array:

use std::collections::BTreeMap;

let solar_distance = BTreeMap::from([
    ("Mercury", 0.4),
    ("Venus", 0.7),
    ("Earth", 1.0),
    ("Mars", 1.5),
]);
Run

BTreeMap implements an Entry API, which allows for complex methods of getting, setting, updating and removing keys and their values:

use std::collections::BTreeMap;

// type inference lets us omit an explicit type signature (which
// would be `BTreeMap<&str, u8>` in this example).
let mut player_stats = BTreeMap::new();

fn random_stat_buff() -> u8 {
    // could actually return some random value here - let's just return
    // some fixed value for now
    42
}

// insert a key only if it doesn't already exist
player_stats.entry("health").or_insert(100);

// insert a key using a function that provides a new value only if it
// doesn't already exist
player_stats.entry("defence").or_insert_with(random_stat_buff);

// update a key, guarding against the key possibly not being set
let stat = player_stats.entry("attack").or_insert(100);
*stat += random_stat_buff();

// modify an entry before an insert with in-place mutation
player_stats.entry("mana").and_modify(|mana| *mana += 200).or_insert(100);
Run

Implementations§

source§

impl<K, V> BTreeMap<K, V, Global>

const: 1.66.0 · source

pub const fn new() -> BTreeMap<K, V, Global>

Makes a new, empty BTreeMap.

Does not allocate anything on its own.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();

// entries can now be inserted into the empty map
map.insert(1, "a");
Run
source§

impl<K, V, A> BTreeMap<K, V, A>where A: Allocator + Clone,

source

pub fn clear(&mut self)

Clears the map, removing all elements.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, "a");
a.clear();
assert!(a.is_empty());
Run
source

pub const fn new_in(alloc: A) -> BTreeMap<K, V, A>

🔬This is a nightly-only experimental API. (btreemap_alloc #32838)

Makes a new empty BTreeMap with a reasonable choice for B.

Examples
use std::collections::BTreeMap;
use std::alloc::Global;

let mut map = BTreeMap::new_in(Global);

// entries can now be inserted into the empty map
map.insert(1, "a");
Run
source§

impl<K, V, A> BTreeMap<K, V, A>where A: Allocator + Clone,

source

pub fn get<Q>(&self, key: &Q) -> Option<&V>where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Returns a reference to the value corresponding to the key.

The key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);
Run
1.40.0 · source

pub fn get_key_value<Q>(&self, k: &Q) -> Option<(&K, &V)>where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Returns the key-value pair corresponding to the supplied key.

The supplied key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
assert_eq!(map.get_key_value(&2), None);
Run
1.66.0 · source

pub fn first_key_value(&self) -> Option<(&K, &V)>where K: Ord,

Returns the first key-value pair in the map. The key in this pair is the minimum key in the map.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
assert_eq!(map.first_key_value(), None);
map.insert(1, "b");
map.insert(2, "a");
assert_eq!(map.first_key_value(), Some((&1, &"b")));
Run
1.66.0 · source

pub fn first_entry(&mut self) -> Option<OccupiedEntry<'_, K, V, A>>where K: Ord,

Returns the first entry in the map for in-place manipulation. The key of this entry is the minimum key in the map.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
map.insert(2, "b");
if let Some(mut entry) = map.first_entry() {
    if *entry.key() > 0 {
        entry.insert("first");
    }
}
assert_eq!(*map.get(&1).unwrap(), "first");
assert_eq!(*map.get(&2).unwrap(), "b");
Run
1.66.0 · source

pub fn pop_first(&mut self) -> Option<(K, V)>where K: Ord,

Removes and returns the first element in the map. The key of this element is the minimum key that was in the map.

Examples

Draining elements in ascending order, while keeping a usable map each iteration.

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
map.insert(2, "b");
while let Some((key, _val)) = map.pop_first() {
    assert!(map.iter().all(|(k, _v)| *k > key));
}
assert!(map.is_empty());
Run
1.66.0 · source

pub fn last_key_value(&self) -> Option<(&K, &V)>where K: Ord,

Returns the last key-value pair in the map. The key in this pair is the maximum key in the map.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "b");
map.insert(2, "a");
assert_eq!(map.last_key_value(), Some((&2, &"a")));
Run
1.66.0 · source

pub fn last_entry(&mut self) -> Option<OccupiedEntry<'_, K, V, A>>where K: Ord,

Returns the last entry in the map for in-place manipulation. The key of this entry is the maximum key in the map.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
map.insert(2, "b");
if let Some(mut entry) = map.last_entry() {
    if *entry.key() > 0 {
        entry.insert("last");
    }
}
assert_eq!(*map.get(&1).unwrap(), "a");
assert_eq!(*map.get(&2).unwrap(), "last");
Run
1.66.0 · source

pub fn pop_last(&mut self) -> Option<(K, V)>where K: Ord,

Removes and returns the last element in the map. The key of this element is the maximum key that was in the map.

Examples

Draining elements in descending order, while keeping a usable map each iteration.

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
map.insert(2, "b");
while let Some((key, _val)) = map.pop_last() {
    assert!(map.iter().all(|(k, _v)| *k < key));
}
assert!(map.is_empty());
Run
source

pub fn contains_key<Q>(&self, key: &Q) -> boolwhere K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Returns true if the map contains a value for the specified key.

The key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
assert_eq!(map.contains_key(&1), true);
assert_eq!(map.contains_key(&2), false);
Run
source

pub fn get_mut<Q>(&mut self, key: &Q) -> Option<&mut V>where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Returns a mutable reference to the value corresponding to the key.

The key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
if let Some(x) = map.get_mut(&1) {
    *x = "b";
}
assert_eq!(map[&1], "b");
Run
source

pub fn insert(&mut self, key: K, value: V) -> Option<V>where K: Ord,

Inserts a key-value pair into the map.

If the map did not have this key present, None is returned.

If the map did have this key present, the value is updated, and the old value is returned. The key is not updated, though; this matters for types that can be == without being identical. See the module-level documentation for more.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
assert_eq!(map.insert(37, "a"), None);
assert_eq!(map.is_empty(), false);

map.insert(37, "b");
assert_eq!(map.insert(37, "c"), Some("b"));
assert_eq!(map[&37], "c");
Run
source

pub fn try_insert( &mut self, key: K, value: V ) -> Result<&mut V, OccupiedError<'_, K, V, A>>where K: Ord,

🔬This is a nightly-only experimental API. (map_try_insert #82766)

Tries to insert a key-value pair into the map, and returns a mutable reference to the value in the entry.

If the map already had this key present, nothing is updated, and an error containing the occupied entry and the value is returned.

Examples
#![feature(map_try_insert)]

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
assert_eq!(map.try_insert(37, "a").unwrap(), &"a");

let err = map.try_insert(37, "b").unwrap_err();
assert_eq!(err.entry.key(), &37);
assert_eq!(err.entry.get(), &"a");
assert_eq!(err.value, "b");
Run
source

pub fn remove<Q>(&mut self, key: &Q) -> Option<V>where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Removes a key from the map, returning the value at the key if the key was previously in the map.

The key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
assert_eq!(map.remove(&1), Some("a"));
assert_eq!(map.remove(&1), None);
Run
1.45.0 · source

pub fn remove_entry<Q>(&mut self, key: &Q) -> Option<(K, V)>where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Removes a key from the map, returning the stored key and value if the key was previously in the map.

The key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
assert_eq!(map.remove_entry(&1), Some((1, "a")));
assert_eq!(map.remove_entry(&1), None);
Run
1.53.0 · source

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

Retains only the elements specified by the predicate.

In other words, remove all pairs (k, v) for which f(&k, &mut v) returns false. The elements are visited in ascending key order.

Examples
use std::collections::BTreeMap;

let mut map: BTreeMap<i32, i32> = (0..8).map(|x| (x, x*10)).collect();
// Keep only the elements with even-numbered keys.
map.retain(|&k, _| k % 2 == 0);
assert!(map.into_iter().eq(vec![(0, 0), (2, 20), (4, 40), (6, 60)]));
Run
1.11.0 · source

pub fn append(&mut self, other: &mut BTreeMap<K, V, A>)where K: Ord, A: Clone,

Moves all elements from other into self, leaving other empty.

If a key from other is already present in self, the respective value from self will be overwritten with the respective value from other.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, "a");
a.insert(2, "b");
a.insert(3, "c"); // Note: Key (3) also present in b.

let mut b = BTreeMap::new();
b.insert(3, "d"); // Note: Key (3) also present in a.
b.insert(4, "e");
b.insert(5, "f");

a.append(&mut b);

assert_eq!(a.len(), 5);
assert_eq!(b.len(), 0);

assert_eq!(a[&1], "a");
assert_eq!(a[&2], "b");
assert_eq!(a[&3], "d"); // Note: "c" has been overwritten.
assert_eq!(a[&4], "e");
assert_eq!(a[&5], "f");
Run
1.17.0 · source

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

Constructs a double-ended iterator over a sub-range of elements in the map. The simplest way is to use the range syntax min..max, thus range(min..max) will yield elements from min (inclusive) to max (exclusive). The range may also be entered as (Bound<T>, Bound<T>), so for example range((Excluded(4), Included(10))) will yield a left-exclusive, right-inclusive range from 4 to 10.

Panics

Panics if range start > end. Panics if range start == end and both bounds are Excluded.

Examples
use std::collections::BTreeMap;
use std::ops::Bound::Included;

let mut map = BTreeMap::new();
map.insert(3, "a");
map.insert(5, "b");
map.insert(8, "c");
for (&key, &value) in map.range((Included(&4), Included(&8))) {
    println!("{key}: {value}");
}
assert_eq!(Some((&5, &"b")), map.range(4..).next());
Run
1.17.0 · source

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

Constructs a mutable double-ended iterator over a sub-range of elements in the map. The simplest way is to use the range syntax min..max, thus range(min..max) will yield elements from min (inclusive) to max (exclusive). The range may also be entered as (Bound<T>, Bound<T>), so for example range((Excluded(4), Included(10))) will yield a left-exclusive, right-inclusive range from 4 to 10.

Panics

Panics if range start > end. Panics if range start == end and both bounds are Excluded.

Examples
use std::collections::BTreeMap;

let mut map: BTreeMap<&str, i32> =
    [("Alice", 0), ("Bob", 0), ("Carol", 0), ("Cheryl", 0)].into();
for (_, balance) in map.range_mut("B".."Cheryl") {
    *balance += 100;
}
for (name, balance) in &map {
    println!("{name} => {balance}");
}
Run
source

pub fn entry(&mut self, key: K) -> Entry<'_, K, V, A>where K: Ord,

Gets the given key’s corresponding entry in the map for in-place manipulation.

Examples
use std::collections::BTreeMap;

let mut count: BTreeMap<&str, usize> = BTreeMap::new();

// count the number of occurrences of letters in the vec
for x in ["a", "b", "a", "c", "a", "b"] {
    count.entry(x).and_modify(|curr| *curr += 1).or_insert(1);
}

assert_eq!(count["a"], 3);
assert_eq!(count["b"], 2);
assert_eq!(count["c"], 1);
Run
1.11.0 · source

pub fn split_off<Q>(&mut self, key: &Q) -> BTreeMap<K, V, A>where Q: Ord + ?Sized, K: Borrow<Q> + Ord, A: Clone,

Splits the collection into two at the given key. Returns everything after the given key, including the key.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, "a");
a.insert(2, "b");
a.insert(3, "c");
a.insert(17, "d");
a.insert(41, "e");

let b = a.split_off(&3);

assert_eq!(a.len(), 2);
assert_eq!(b.len(), 3);

assert_eq!(a[&1], "a");
assert_eq!(a[&2], "b");

assert_eq!(b[&3], "c");
assert_eq!(b[&17], "d");
assert_eq!(b[&41], "e");
Run
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pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, K, V, F, A> where K: Ord, F: FnMut(&K, &mut V) -> bool,

🔬This is a nightly-only experimental API. (btree_extract_if #70530)

Creates an iterator that visits all elements (key-value pairs) in ascending key order and uses a closure to determine if an element should be removed. If the closure returns true, the element is removed from the map and yielded. If the closure returns false, or panics, the element remains in the map and will not be yielded.

The iterator also lets you mutate the value of each element in the closure, regardless of whether you choose to keep or remove it.

If the returned ExtractIf is not exhausted, e.g. because it is dropped without iterating or the iteration short-circuits, then the remaining elements will be retained. Use retain with a negated predicate if you do not need the returned iterator.

Examples

Splitting a map into even and odd keys, reusing the original map:

#![feature(btree_extract_if)]
use std::collections::BTreeMap;

let mut map: BTreeMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
let evens: BTreeMap<_, _> = map.extract_if(|k, _v| k % 2 == 0).collect();
let odds = map;
assert_eq!(evens.keys().copied().collect::<Vec<_>>(), [0, 2, 4, 6]);
assert_eq!(odds.keys().copied().collect::<Vec<_>>(), [1, 3, 5, 7]);
Run
1.54.0 · source

pub fn into_keys(self) -> IntoKeys<K, V, A>

Creates a consuming iterator visiting all the keys, in sorted order. The map cannot be used after calling this. The iterator element type is K.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(2, "b");
a.insert(1, "a");

let keys: Vec<i32> = a.into_keys().collect();
assert_eq!(keys, [1, 2]);
Run
1.54.0 · source

pub fn into_values(self) -> IntoValues<K, V, A>

Creates a consuming iterator visiting all the values, in order by key. The map cannot be used after calling this. The iterator element type is V.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, "hello");
a.insert(2, "goodbye");

let values: Vec<&str> = a.into_values().collect();
assert_eq!(values, ["hello", "goodbye"]);
Run
source§

impl<K, V, A> BTreeMap<K, V, A>where A: Allocator + Clone,

source

pub fn iter(&self) -> Iter<'_, K, V>

Gets an iterator over the entries of the map, sorted by key.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(3, "c");
map.insert(2, "b");
map.insert(1, "a");

for (key, value) in map.iter() {
    println!("{key}: {value}");
}

let (first_key, first_value) = map.iter().next().unwrap();
assert_eq!((*first_key, *first_value), (1, "a"));
Run
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pub fn iter_mut(&mut self) -> IterMut<'_, K, V>

Gets a mutable iterator over the entries of the map, sorted by key.

Examples
use std::collections::BTreeMap;

let mut map = BTreeMap::from([
   ("a", 1),
   ("b", 2),
   ("c", 3),
]);

// add 10 to the value if the key isn't "a"
for (key, value) in map.iter_mut() {
    if key != &"a" {
        *value += 10;
    }
}
Run
source

pub fn keys(&self) -> Keys<'_, K, V>

Gets an iterator over the keys of the map, in sorted order.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(2, "b");
a.insert(1, "a");

let keys: Vec<_> = a.keys().cloned().collect();
assert_eq!(keys, [1, 2]);
Run
source

pub fn values(&self) -> Values<'_, K, V>

Gets an iterator over the values of the map, in order by key.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, "hello");
a.insert(2, "goodbye");

let values: Vec<&str> = a.values().cloned().collect();
assert_eq!(values, ["hello", "goodbye"]);
Run
1.10.0 · source

pub fn values_mut(&mut self) -> ValuesMut<'_, K, V>

Gets a mutable iterator over the values of the map, in order by key.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, String::from("hello"));
a.insert(2, String::from("goodbye"));

for value in a.values_mut() {
    value.push_str("!");
}

let values: Vec<String> = a.values().cloned().collect();
assert_eq!(values, [String::from("hello!"),
                    String::from("goodbye!")]);
Run
const: unstable · source

pub fn len(&self) -> usize

Returns the number of elements in the map.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
assert_eq!(a.len(), 0);
a.insert(1, "a");
assert_eq!(a.len(), 1);
Run
const: unstable · source

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

Examples
use std::collections::BTreeMap;

let mut a = BTreeMap::new();
assert!(a.is_empty());
a.insert(1, "a");
assert!(!a.is_empty());
Run
source

pub fn lower_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>where K: Borrow<Q> + Ord, Q: Ord,

🔬This is a nightly-only experimental API. (btree_cursors #107540)

Returns a Cursor pointing at the first element that is above the given bound.

If no such element exists then a cursor pointing at the “ghost” non-element is returned.

Passing Bound::Unbounded will return a cursor pointing at the first element of the map.

Examples
#![feature(btree_cursors)]

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, "c");
let cursor = a.lower_bound(Bound::Included(&2));
assert_eq!(cursor.key(), Some(&2));
let cursor = a.lower_bound(Bound::Excluded(&2));
assert_eq!(cursor.key(), Some(&3));
Run
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pub fn lower_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A>where K: Borrow<Q> + Ord, Q: Ord,

🔬This is a nightly-only experimental API. (btree_cursors #107540)

Returns a CursorMut pointing at the first element that is above the given bound.

If no such element exists then a cursor pointing at the “ghost” non-element is returned.

Passing Bound::Unbounded will return a cursor pointing at the first element of the map.

Examples
#![feature(btree_cursors)]

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, "c");
let cursor = a.lower_bound_mut(Bound::Included(&2));
assert_eq!(cursor.key(), Some(&2));
let cursor = a.lower_bound_mut(Bound::Excluded(&2));
assert_eq!(cursor.key(), Some(&3));
Run
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pub fn upper_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>where K: Borrow<Q> + Ord, Q: Ord,

🔬This is a nightly-only experimental API. (btree_cursors #107540)

Returns a Cursor pointing at the last element that is below the given bound.

If no such element exists then a cursor pointing at the “ghost” non-element is returned.

Passing Bound::Unbounded will return a cursor pointing at the last element of the map.

Examples
#![feature(btree_cursors)]

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, "c");
let cursor = a.upper_bound(Bound::Included(&3));
assert_eq!(cursor.key(), Some(&3));
let cursor = a.upper_bound(Bound::Excluded(&3));
assert_eq!(cursor.key(), Some(&2));
Run
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pub fn upper_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A>where K: Borrow<Q> + Ord, Q: Ord,

🔬This is a nightly-only experimental API. (btree_cursors #107540)

Returns a CursorMut pointing at the last element that is below the given bound.

If no such element exists then a cursor pointing at the “ghost” non-element is returned.

Passing Bound::Unbounded will return a cursor pointing at the last element of the map.

Examples
#![feature(btree_cursors)]

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, "c");
let cursor = a.upper_bound_mut(Bound::Included(&3));
assert_eq!(cursor.key(), Some(&3));
let cursor = a.upper_bound_mut(Bound::Excluded(&3));
assert_eq!(cursor.key(), Some(&2));
Run

Trait Implementations§

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impl<K, V, A> Clone for BTreeMap<K, V, A>where K: Clone, V: Clone, A: Allocator + Clone,

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fn clone(&self) -> BTreeMap<K, V, A>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<K, V, A> Debug for BTreeMap<K, V, A>where K: Debug, V: Debug, A: Allocator + Clone,

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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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impl<K, V> Default for BTreeMap<K, V, Global>

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fn default() -> BTreeMap<K, V, Global>

Creates an empty BTreeMap.

1.7.0 · source§

impl<K, V, A> Drop for BTreeMap<K, V, A>where A: Allocator + Clone,

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fn drop(&mut self)

Executes the destructor for this type. Read more
1.2.0 · source§

impl<'a, K, V, A> Extend<(&'a K, &'a V)> for BTreeMap<K, V, A>where K: Ord + Copy, V: Copy, A: Allocator + Clone,

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fn extend<I>(&mut self, iter: I)where I: IntoIterator<Item = (&'a K, &'a V)>,

Extends a collection with the contents of an iterator. Read more
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fn extend_one(&mut self, _: (&'a K, &'a V))

🔬This is a nightly-only experimental API. (extend_one #72631)
Extends a collection with exactly one element.
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fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
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impl<K, V, A> Extend<(K, V)> for BTreeMap<K, V, A>where K: Ord, A: Allocator + Clone,

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fn extend<T>(&mut self, iter: T)where T: IntoIterator<Item = (K, V)>,

Extends a collection with the contents of an iterator. Read more
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fn extend_one(&mut self, _: (K, V))

🔬This is a nightly-only experimental API. (extend_one #72631)
Extends a collection with exactly one element.
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fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.56.0 · source§

impl<K, V, const N: usize> From<[(K, V); N]> for BTreeMap<K, V, Global>where K: Ord,

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fn from(arr: [(K, V); N]) -> BTreeMap<K, V, Global>

Converts a [(K, V); N] into a BTreeMap<(K, V)>.

use std::collections::BTreeMap;

let map1 = BTreeMap::from([(1, 2), (3, 4)]);
let map2: BTreeMap<_, _> = [(1, 2), (3, 4)].into();
assert_eq!(map1, map2);
Run
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impl<K, V> FromIterator<(K, V)> for BTreeMap<K, V, Global>where K: Ord,

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fn from_iter<T>(iter: T) -> BTreeMap<K, V, Global>where T: IntoIterator<Item = (K, V)>,

Creates a value from an iterator. Read more
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impl<K, V, A> Hash for BTreeMap<K, V, A>where K: Hash, V: Hash, A: Allocator + Clone,

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fn hash<H>(&self, state: &mut H)where H: Hasher,

Feeds this value into the given Hasher. Read more
1.3.0 · source§

fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl<K, Q, V, A> Index<&Q> for BTreeMap<K, V, A>where A: Allocator + Clone, K: Borrow<Q> + Ord, Q: Ord + ?Sized,

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fn index(&self, key: &Q) -> &V

Returns a reference to the value corresponding to the supplied key.

Panics

Panics if the key is not present in the BTreeMap.

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type Output = V

The returned type after indexing.
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impl<'a, K, V, A> IntoIterator for &'a BTreeMap<K, V, A>where A: Allocator + Clone,

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type Item = (&'a K, &'a V)

The type of the elements being iterated over.
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type IntoIter = Iter<'a, K, V>

Which kind of iterator are we turning this into?
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fn into_iter(self) -> Iter<'a, K, V>

Creates an iterator from a value. Read more
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impl<'a, K, V, A> IntoIterator for &'a mut BTreeMap<K, V, A>where A: Allocator + Clone,

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type Item = (&'a K, &'a mut V)

The type of the elements being iterated over.
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type IntoIter = IterMut<'a, K, V>

Which kind of iterator are we turning this into?
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fn into_iter(self) -> IterMut<'a, K, V>

Creates an iterator from a value. Read more
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impl<K, V, A> IntoIterator for BTreeMap<K, V, A>where A: Allocator + Clone,

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type Item = (K, V)

The type of the elements being iterated over.
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type IntoIter = IntoIter<K, V, A>

Which kind of iterator are we turning this into?
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fn into_iter(self) -> IntoIter<K, V, A>

Creates an iterator from a value. Read more
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impl<K, V, A> Ord for BTreeMap<K, V, A>where K: Ord, V: Ord, A: Allocator + Clone,

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fn cmp(&self, other: &BTreeMap<K, V, A>) -> Ordering

This method returns an Ordering between self and other. Read more
1.21.0 · source§

fn max(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · source§

fn min(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · source§

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval. Read more
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impl<K, V, A> PartialEq<BTreeMap<K, V, A>> for BTreeMap<K, V, A>where K: PartialEq<K>, V: PartialEq<V>, A: Allocator + Clone,

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fn eq(&self, other: &BTreeMap<K, V, A>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<K, V, A> PartialOrd<BTreeMap<K, V, A>> for BTreeMap<K, V, A>where K: PartialOrd<K>, V: PartialOrd<V>, A: Allocator + Clone,

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fn partial_cmp(&self, other: &BTreeMap<K, V, A>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl<K, V, A> Eq for BTreeMap<K, V, A>where K: Eq, V: Eq, A: Allocator + Clone,

1.64.0 · source§

impl<K, V, A> UnwindSafe for BTreeMap<K, V, A>where A: Allocator + Clone + UnwindSafe, K: RefUnwindSafe, V: RefUnwindSafe,

Auto Trait Implementations§

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impl<K, V, A> RefUnwindSafe for BTreeMap<K, V, A>where A: RefUnwindSafe, K: RefUnwindSafe, V: RefUnwindSafe,

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impl<K, V, A> Send for BTreeMap<K, V, A>where A: Send, K: Send, V: Send,

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impl<K, V, A> Sync for BTreeMap<K, V, A>where A: Sync, K: Sync, V: Sync,

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impl<K, V, A> Unpin for BTreeMap<K, V, A>where A: Unpin,

Blanket Implementations§

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impl<T> Any for Twhere T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for Twhere T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for Twhere U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for Twhere T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.