description

# Map<K, V> class Null safety

A collection of key/value pairs, from which you retrieve a value using its associated key.

There is a finite number of keys in the map, and each key has exactly one value associated with it.

Maps, and their keys and values, can be iterated. The order of iteration is defined by the individual type of map. Examples:

- The plain HashMap is unordered (no order is guaranteed),
- the LinkedHashMap iterates in key insertion order,
- and a sorted map like SplayTreeMap iterates the keys in sorted order.

It is generally not allowed to modify the map (add or remove keys) while an operation is being performed on the map, for example in functions called during a forEach or putIfAbsent call. Modifying the map while iterating the keys or values may also break the iteration.

It is generally not allowed to modify the equality of keys (and thus not their hashcode) while they are in the map. Some specialized subtypes may be more permissive, in which case they should document this behavior.

Implementers
  - HashMap
  - HttpSession
  - LinkedHashMap
  - MapMixin
  - MapView

## Constructors

Map()
  Creates a Map instance with the default implementation, LinkedHashMap. [...]
  factory
Map.from(Map other)
  Creates a LinkedHashMap instance that contains all key/value pairs of `other`. [...]
  factory
Map.fromEntries(Iterable<MapEntry<K, V>> entries)
  Creates a new map and adds all entries. [...]
  factory
Map.fromIterable(Iterable iterable, {K key(dynamic element), V value(dynamic element)})
  Creates a Map instance in which the keys and values are computed from the `iterable`. [...]
  factory
Map.fromIterables(Iterable<K> keys, Iterable<V> values)
  Creates a Map instance associating the given `keys` to `values`. [...]
  factory
Map.identity()
  Creates an identity map with the default implementation, LinkedHashMap. [...]
  factory
Map.of(Map<K, V> other)
  Creates a LinkedHashMap with the same keys and values as `other`. [...]
  factory
Map.unmodifiable(Map other)
  Creates an unmodifiable hash based map containing the entries of `other`. [...]
  factory

## Properties

entries → Iterable<MapEntry<K, V>>
  The map entries of this.
  read-only
hashCode → int
  The hash code for this object. [...]
  read-only, inherited
isEmpty → bool
  Returns true if there is no key/value pair in the map.
  read-only
isNotEmpty → bool
  Returns true if there is at least one key/value pair in the map.
  read-only
keys → Iterable<K>
  The keys of this. [...]
  read-only
length → int
  The number of key/value pairs in the map.
  read-only
runtimeType → Type
  A representation of the runtime type of the object.
  read-only, inherited
values → Iterable<V>
  The values of this. [...]
  read-only

## Methods

addAll(Map<K, V> other) → void
  Adds all key/value pairs of `other` to this map. [...]
addEntries(Iterable<MapEntry<K, V>> newEntries) → void
  Adds all key/value pairs of `newEntries` to this map. [...]
cast<RK, RV>() → Map<RK, RV>
  Provides a view of this map as having `RK` keys and `RV` instances, if necessary. [...]
clear() → void
  Removes all pairs from the map. [...]
containsKey(Object? key) → bool
  Returns true if this map contains the given `key`. [...]
containsValue(Object? value) → bool
  Returns true if this map contains the given `value`. [...]
forEach(void f(K key, V value)) → void
  Applies `f` to each key/value pair of the map. [...]
map<K2, V2>(MapEntry<K2, V2> f(K key, V value)) → Map<K2, V2>
  Returns a new map where all entries of this map are transformed by the given `f` function.
noSuchMethod(Invocation invocation) → dynamic
  Invoked when a non-existent method or property is accessed. [...]
  inherited
putIfAbsent(K key, V ifAbsent()) → V
  Look up the value of `key`, or add a new value if it isn't there. [...]
remove(Object? key) → V?
  Removes `key` and its associated value, if present, from the map. [...]
removeWhere(bool predicate(K key, V value)) → void
  Removes all entries of this map that satisfy the given `predicate`.
toString() → String
  Returns a string representation of this object.
  inherited
update(K key, V update(V value), {V ifAbsent()}) → V
  Updates the value for the provided `key`. [...]
updateAll(V update(K key, V value)) → void
  Updates all values. [...]

## Operators

operator ==(Object other) → bool
  The equality operator. [...]
  inherited
operator [](Object? key) → V?
  Returns the value for the given `key` or null if `key` is not in the map. [...]
operator []=(K key, V value) → void
  Associates the `key` with the given `value`. [...]

## Static Methods

castFrom<K, V, K2, V2>(Map<K, V> source) → Map<K2, V2>
  Adapts `source` to be a `Map<K2, V2>`. [...]