Returns a reference to the map's BuildHasher
.
use std::collections::HashMap;
use std::collections::hash_map::RandomState;
let hasher = RandomState::new();
let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
let hasher: &RandomState = map.hasher();
Returns the number of elements the map can hold without reallocating.
This number is a lower bound; the HashMap<K, V>
might be able to hold
more, but is guaranteed to be able to hold at least this many.
use std::collections::HashMap;
let map: HashMap<i32, i32> = HashMap::with_capacity(100);
assert!(map.capacity() >= 100);
An iterator visiting all keys in arbitrary order.
The iterator element type is &'a K
.
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
for key in map.keys() {
println!("{}", key);
}
An iterator visiting all values in arbitrary order.
The iterator element type is &'a V
.
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
for val in map.values() {
println!("{}", val);
}
An iterator visiting all key-value pairs in arbitrary order.
The iterator element type is (&'a K, &'a V)
.
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
for (key, val) in map.iter() {
println!("key: {} val: {}", key, val);
}
Returns the number of elements in the map.
use std::collections::HashMap;
let mut a = HashMap::new();
assert_eq!(a.len(), 0);
a.insert(1, "a");
assert_eq!(a.len(), 1);
Returns true if the map contains no elements.
use std::collections::HashMap;
let mut a = HashMap::new();
assert!(a.is_empty());
a.insert(1, "a");
assert!(!a.is_empty());
Returns a reference to the value corresponding to the key.
The key may be any borrowed form of the map's key type, but
Hash
and Eq
on the borrowed form must match those for
the key type.
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);
🔬 This is a nightly-only experimental API. (map_get_key_value
)
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
Hash
and Eq
on the borrowed form must match those for
the key type.
#![feature(map_get_key_value)]
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
assert_eq!(map.get_key_value(&2), None);
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
Hash
and Eq
on the borrowed form must match those for
the key type.
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.contains_key(&1), true);
assert_eq!(map.contains_key(&2), false);