com.google.javascript.rhino

Class HamtPMap<K,V>

java.lang.Object

com.google.javascript.rhino.HamtPMap<K,V>

All Implemented Interfaces:

PMap<K,V>, java.io.Serializable

public final class HamtPMap<K,V>
extends java.lang.Object
implements PMap<K,V>, java.io.Serializable

An immutable sorted map with efficient (persistent) updates.

Uses a hash array mapped trie: http://en.wikipedia.org/wiki/Hash_array_mapped_trie.

This implementation stores the bare minimum in each node: a key (with its hash), value, mask, and children. It is also optimized to take maximum advantage of binary operations on shared trees. Specifically, reconcile(com.google.javascript.rhino.PMap<K, V>, com.google.javascript.rhino.PMap.BiFunction<V, V, V>) avoids recursing into entire subtrees if they are identical objects. Null keys and values are not allowed. The implementation special-cases away the EMPTY map as soon as possible, using 'null' instead for all the logic (since EMPTY violates the invariant that key and value are non-null). Finally, we maintain an invariant that the entry with the smallest hash code is always at the root of the tree, which avoids almost all extra tree rebuilding during binary operations.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface com.google.javascript.rhino.PMap

PMap.BiFunction<A,B,C>, PMap.BiPredicate<A,B>

Method Summary

Modifier and Type	Method and Description
static <K,V> HamtPMap<K,V>	empty() Returns an empty map.
boolean	equivalent(PMap<K,V> that, PMap.BiPredicate<V,V> equivalence) Checks equality recursively based on the given equivalence.
V	get(K key) Retrieves the value associated with the given key from the map, or returns null if it is not present.
boolean	isEmpty() Returns whether this map is empty.
HamtPMap<K,V>	minus(K key) Returns a new map with the given key removed.
HamtPMap<K,V>	plus(K key, V value) Returns a new map with the given key-value pair added.
HamtPMap<K,V>	reconcile(PMap<K,V> that, PMap.BiFunction<V,V,V> joiner) Performs a reconcile operation.
java.lang.String	toString()
java.lang.Iterable<V>	values() Returns an iterable for a (possibly null) tree.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

empty

public static <K,V> HamtPMap<K,V> empty()

Returns an empty map.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

isEmpty

public boolean isEmpty()

Returns whether this map is empty.

Specified by:

isEmpty in interface PMap<K,V>

values

public java.lang.Iterable<V> values()

Returns an iterable for a (possibly null) tree.

Specified by:

values in interface PMap<K,V>

get

public V get(K key)

Retrieves the value associated with the given key from the map, or returns null if it is not present.

Specified by:

get in interface PMap<K,V>

plus

public HamtPMap<K,V> plus(K key,
                          V value)

Returns a new map with the given key-value pair added. If the value is already present, then this same map will be returned.

Specified by:

plus in interface PMap<K,V>

minus

public HamtPMap<K,V> minus(K key)

Returns a new map with the given key removed. If the key was not present in the first place, then this same map will be returned.

Specified by:

minus in interface PMap<K,V>

reconcile

public HamtPMap<K,V> reconcile(PMap<K,V> that,
                               PMap.BiFunction<V,V,V> joiner)

Description copied from interface: PMap

Performs a reconcile operation. The joiner is called for all conflicting (based on Object#equals) values between the two maps, or if a key is missing from one map. If both maps have equal values then that value will be added directly to the result without calling the joiner. If the joiner returns null, then the entry is removed. The first argument to the joined always comes from 'this' map, and the second is always from 'that'. Note that that map must be the same implementation.

Specified by:

reconcile in interface PMap<K,V>

equivalent

public boolean equivalent(PMap<K,V> that,
                          PMap.BiPredicate<V,V> equivalence)

Checks equality recursively based on the given equivalence. Short-circuits as soon as a 'false' result is found.

Specified by:

equivalent in interface PMap<K,V>