Enum hashbrown::hash_map::Entry

source · [−]
pub enum Entry<'a, K, V, S, A = Global>where
    A: Allocator + Clone,{
    Occupied(OccupiedEntry<'a, K, V, S, A>),
    Vacant(VacantEntry<'a, K, V, S, A>),
}
Expand description

A view into a single entry in a map, which may either be vacant or occupied.

This enum is constructed from the entry method on HashMap.

Examples

use hashbrown::hash_map::{Entry, HashMap, OccupiedEntry};

let mut map = HashMap::new();
map.extend([("a", 10), ("b", 20), ("c", 30)]);
assert_eq!(map.len(), 3);

// Existing key (insert)
let entry: Entry<_, _, _> = map.entry("a");
let _raw_o: OccupiedEntry<_, _, _> = entry.insert(1);
assert_eq!(map.len(), 3);
// Nonexistent key (insert)
map.entry("d").insert(4);

// Existing key (or_insert)
let v = map.entry("b").or_insert(2);
assert_eq!(std::mem::replace(v, 2), 20);
// Nonexistent key (or_insert)
map.entry("e").or_insert(5);

// Existing key (or_insert_with)
let v = map.entry("c").or_insert_with(|| 3);
assert_eq!(std::mem::replace(v, 3), 30);
// Nonexistent key (or_insert_with)
map.entry("f").or_insert_with(|| 6);

println!("Our HashMap: {:?}", map);

let mut vec: Vec<_> = map.iter().map(|(&k, &v)| (k, v)).collect();
// The `Iter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3), ("d", 4), ("e", 5), ("f", 6)]);

Variants

Occupied(OccupiedEntry<'a, K, V, S, A>)

An occupied entry.

Examples

use hashbrown::hash_map::{Entry, HashMap};
let mut map: HashMap<_, _> = [("a", 100), ("b", 200)].into();

match map.entry("a") {
    Entry::Vacant(_) => unreachable!(),
    Entry::Occupied(_) => { }
}

Vacant(VacantEntry<'a, K, V, S, A>)

A vacant entry.

Examples

use hashbrown::hash_map::{Entry, HashMap};
let mut map: HashMap<&str, i32> = HashMap::new();

match map.entry("a") {
    Entry::Occupied(_) => unreachable!(),
    Entry::Vacant(_) => { }
}

Implementations

Sets the value of the entry, and returns an OccupiedEntry.

Examples
use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();
let entry = map.entry("horseyland").insert(37);

assert_eq!(entry.key(), &"horseyland");

Ensures a value is in the entry by inserting the default if empty, and returns a mutable reference to the value in the entry.

Examples
use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();

// nonexistent key
map.entry("poneyland").or_insert(3);
assert_eq!(map["poneyland"], 3);

// existing key
*map.entry("poneyland").or_insert(10) *= 2;
assert_eq!(map["poneyland"], 6);

Ensures a value is in the entry by inserting the result of the default function if empty, and returns a mutable reference to the value in the entry.

Examples
use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();

// nonexistent key
map.entry("poneyland").or_insert_with(|| 3);
assert_eq!(map["poneyland"], 3);

// existing key
*map.entry("poneyland").or_insert_with(|| 10) *= 2;
assert_eq!(map["poneyland"], 6);

Ensures a value is in the entry by inserting, if empty, the result of the default function. This method allows for generating key-derived values for insertion by providing the default function a reference to the key that was moved during the .entry(key) method call.

The reference to the moved key is provided so that cloning or copying the key is unnecessary, unlike with .or_insert_with(|| ... ).

Examples
use hashbrown::HashMap;

let mut map: HashMap<&str, usize> = HashMap::new();

// nonexistent key
map.entry("poneyland").or_insert_with_key(|key| key.chars().count());
assert_eq!(map["poneyland"], 9);

// existing key
*map.entry("poneyland").or_insert_with_key(|key| key.chars().count() * 10) *= 2;
assert_eq!(map["poneyland"], 18);

Returns a reference to this entry’s key.

Examples
use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();
map.entry("poneyland").or_insert(3);
// existing key
assert_eq!(map.entry("poneyland").key(), &"poneyland");
// nonexistent key
assert_eq!(map.entry("horseland").key(), &"horseland");

Provides in-place mutable access to an occupied entry before any potential inserts into the map.

Examples
use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();

map.entry("poneyland")
   .and_modify(|e| { *e += 1 })
   .or_insert(42);
assert_eq!(map["poneyland"], 42);

map.entry("poneyland")
   .and_modify(|e| { *e += 1 })
   .or_insert(42);
assert_eq!(map["poneyland"], 43);
source

pub fn and_replace_entry_with<F>(self, f: F) -> Selfwhere
    F: FnOnce(&K, V) -> Option<V>,

Provides shared access to the key and owned access to the value of an occupied entry and allows to replace or remove it based on the value of the returned option.

Examples
use hashbrown::HashMap;
use hashbrown::hash_map::Entry;

let mut map: HashMap<&str, u32> = HashMap::new();

let entry = map
    .entry("poneyland")
    .and_replace_entry_with(|_k, _v| panic!());

match entry {
    Entry::Vacant(e) => {
        assert_eq!(e.key(), &"poneyland");
    }
    Entry::Occupied(_) => panic!(),
}

map.insert("poneyland", 42);

let entry = map
    .entry("poneyland")
    .and_replace_entry_with(|k, v| {
        assert_eq!(k, &"poneyland");
        assert_eq!(v, 42);
        Some(v + 1)
    });

match entry {
    Entry::Occupied(e) => {
        assert_eq!(e.key(), &"poneyland");
        assert_eq!(e.get(), &43);
    }
    Entry::Vacant(_) => panic!(),
}

assert_eq!(map["poneyland"], 43);

let entry = map
    .entry("poneyland")
    .and_replace_entry_with(|_k, _v| None);

match entry {
    Entry::Vacant(e) => assert_eq!(e.key(), &"poneyland"),
    Entry::Occupied(_) => panic!(),
}

assert!(!map.contains_key("poneyland"));

Ensures a value is in the entry by inserting the default value if empty, and returns a mutable reference to the value in the entry.

Examples
use hashbrown::HashMap;

let mut map: HashMap<&str, Option<u32>> = HashMap::new();

// nonexistent key
map.entry("poneyland").or_default();
assert_eq!(map["poneyland"], None);

map.insert("horseland", Some(3));

// existing key
assert_eq!(map.entry("horseland").or_default(), &mut Some(3));

Trait Implementations

Formats the value using the given formatter. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

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

The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.