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package org.graalvm.collections;

import java.util.Iterator;
import java.util.Map;
import java.util.function.BiFunction;


Memory efficient map data structure that dynamically changes its representation depending on the number of entries and is specially optimized for small number of entries. It keeps elements in a linear list without any hashing when the number of entries is small. Should an actual hash data structure be necessary, it tries to fit the hash value into as few bytes as possible. In contrast to HashMap, it avoids allocating an extra node object per entry and rather keeps values always in a plain array. See EconomicMapImpl for implementation details and exact thresholds when its representation changes. It supports a null value, but it does not support adding or looking up a null key. Operations get and put provide constant-time performance on average if repeatedly performed. They can however trigger an operation growing or compressing the data structure, which is linear in the number of elements. Iteration is also linear in the number of elements. The implementation is not synchronized. If multiple threads want to access the data structure, it requires manual synchronization, for example using Collections.synchronizedMap. There is also no extra precaution to detect concurrent modification while iterating. Different strategies for the equality comparison can be configured by providing a Equivalence configuration object. 
Since:19.0
/**
 * Memory efficient map data structure that dynamically changes its representation depending on the
 * number of entries and is specially optimized for small number of entries. It keeps elements in a
 * linear list without any hashing when the number of entries is small. Should an actual hash data
 * structure be necessary, it tries to fit the hash value into as few bytes as possible. In contrast
 * to {@link java.util.HashMap}, it avoids allocating an extra node object per entry and rather
 * keeps values always in a plain array. See {@link EconomicMapImpl} for implementation details and
 * exact thresholds when its representation changes.
 *
 * It supports a {@code null} value, but it does not support adding or looking up a {@code null}
 * key. Operations {@code get} and {@code put} provide constant-time performance on average if
 * repeatedly performed. They can however trigger an operation growing or compressing the data
 * structure, which is linear in the number of elements. Iteration is also linear in the number of
 * elements.
 *
 * The implementation is not synchronized. If multiple threads want to access the data structure, it
 * requires manual synchronization, for example using {@link java.util.Collections#synchronizedMap}.
 * There is also no extra precaution to detect concurrent modification while iterating.
 *
 * Different strategies for the equality comparison can be configured by providing a
 * {@link Equivalence} configuration object.
 *
 * @since 19.0
 */
public interface EconomicMap<K, V> extends UnmodifiableEconomicMap<K, V> {

    
Associates value with key in this map. If the map previously contained a mapping for key, the old value is replaced by value. While the value may be null, the key must not be {code null}. 
Returns:the previous value associated with key, or null if there was no mapping for key.
Since:19.0
/**
     * Associates {@code value} with {@code key} in this map. If the map previously contained a
     * mapping for {@code key}, the old value is replaced by {@code value}. While the {@code value}
     * may be {@code null}, the {@code key} must not be {code null}.
     *
     * @return the previous value associated with {@code key}, or {@code null} if there was no
     *         mapping for {@code key}.
     * @since 19.0
     */
    V put(K key, V value);

    
If the specified key is not already associated with a value (or is mapped to null) associates it with the given value and returns null, else returns the current value. 
Params:
  • key – key with which the specified value is to be associated
  • value – value to be associated with the specified key
Returns:the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)
Since:20.2
/**
     * If the specified key is not already associated with a value (or is mapped to {@code null})
     * associates it with the given value and returns {@code null}, else returns the current value.
     *
     * @param key key with which the specified value is to be associated
     * @param value value to be associated with the specified key
     *
     * @return the previous value associated with the specified key, or {@code null} if there was no
     *         mapping for the key. (A {@code null} return can also indicate that the map previously
     *         associated {@code null} with the key, if the implementation supports null values.)
     *
     * @since 20.2
     */
    default V putIfAbsent(K key, V value) {
        V v = get(key);
        if (v == null) {
            v = put(key, value);
        }

        return v;
    }

    
Copies all of the mappings from other to this map. 
Since:19.0
/**
     * Copies all of the mappings from {@code other} to this map.
     *
     * @since 19.0
     */
    default void putAll(EconomicMap<K, V> other) {
        MapCursor<K, V> e = other.getEntries();
        while (e.advance()) {
            put(e.getKey(), e.getValue());
        }
    }

    
Copies all of the mappings from other to this map. 
Since:19.0
/**
     * Copies all of the mappings from {@code other} to this map.
     *
     * @since 19.0
     */
    default void putAll(UnmodifiableEconomicMap<? extends K, ? extends V> other) {
        UnmodifiableMapCursor<? extends K, ? extends V> entry = other.getEntries();
        while (entry.advance()) {
            put(entry.getKey(), entry.getValue());
        }
    }

    
Removes all of the mappings from this map. The map will be empty after this call returns.

Since:19.0
/**
     * Removes all of the mappings from this map. The map will be empty after this call returns.
     *
     * @since 19.0
     */
    void clear();

    
Removes the mapping for key from this map if it is present. The map will not contain a mapping for key once the call returns. The key must not be null. 
Returns:the previous value associated with key, or null if there was no mapping for key.
Since:19.0
/**
     * Removes the mapping for {@code key} from this map if it is present. The map will not contain
     * a mapping for {@code key} once the call returns. The {@code key} must not be {@code null}.
     *
     * @return the previous value associated with {@code key}, or {@code null} if there was no
     *         mapping for {@code key}.
     * @since 19.0
     */
    V removeKey(K key);

    
Returns a MapCursor view of the mappings contained in this map. 
Since:19.0
/**
     * Returns a {@link MapCursor} view of the mappings contained in this map.
     *
     * @since 19.0
     */
    @Override
    MapCursor<K, V> getEntries();

    
Replaces each entry's value with the result of invoking function on that entry until all entries have been processed or the function throws an exception. Exceptions thrown by the function are relayed to the caller. 
Since:19.0
/**
     * Replaces each entry's value with the result of invoking {@code function} on that entry until
     * all entries have been processed or the function throws an exception. Exceptions thrown by the
     * function are relayed to the caller.
     *
     * @since 19.0
     */
    void replaceAll(BiFunction<? super K, ? super V, ? extends V> function);

    
Creates a new map that guarantees insertion order on the key set with the default Equivalence.DEFAULT comparison strategy for keys. 
Since:19.0
/**
     * Creates a new map that guarantees insertion order on the key set with the default
     * {@link Equivalence#DEFAULT} comparison strategy for keys.
     *
     * @since 19.0
     */
    static <K, V> EconomicMap<K, V> create() {
        return EconomicMap.create(Equivalence.DEFAULT);
    }

    
Creates a new map that guarantees insertion order on the key set with the default Equivalence.DEFAULT comparison strategy for keys and initializes with a specified capacity. 
Since:19.0
/**
     * Creates a new map that guarantees insertion order on the key set with the default
     * {@link Equivalence#DEFAULT} comparison strategy for keys and initializes with a specified
     * capacity.
     *
     * @since 19.0
     */
    static <K, V> EconomicMap<K, V> create(int initialCapacity) {
        return EconomicMap.create(Equivalence.DEFAULT, initialCapacity);
    }

    
Creates a new map that guarantees insertion order on the key set with the given comparison
strategy for keys.

Since:19.0
/**
     * Creates a new map that guarantees insertion order on the key set with the given comparison
     * strategy for keys.
     *
     * @since 19.0
     */
    static <K, V> EconomicMap<K, V> create(Equivalence strategy) {
        return EconomicMapImpl.create(strategy, false);
    }

    
Creates a new map that guarantees insertion order on the key set with the default Equivalence.DEFAULT comparison strategy for keys and copies all elements from the specified existing map. 
Since:19.0
/**
     * Creates a new map that guarantees insertion order on the key set with the default
     * {@link Equivalence#DEFAULT} comparison strategy for keys and copies all elements from the
     * specified existing map.
     *
     * @since 19.0
     */
    static <K, V> EconomicMap<K, V> create(UnmodifiableEconomicMap<K, V> m) {
        return EconomicMap.create(Equivalence.DEFAULT, m);
    }

    
Creates a new map that guarantees insertion order on the key set and copies all elements from
the specified existing map.

Since:19.0
/**
     * Creates a new map that guarantees insertion order on the key set and copies all elements from
     * the specified existing map.
     *
     * @since 19.0
     */
    static <K, V> EconomicMap<K, V> create(Equivalence strategy, UnmodifiableEconomicMap<K, V> m) {
        return EconomicMapImpl.create(strategy, m, false);
    }

    
Creates a new map that guarantees insertion order on the key set and initializes with a
specified capacity.

Since:19.0
/**
     * Creates a new map that guarantees insertion order on the key set and initializes with a
     * specified capacity.
     *
     * @since 19.0
     */
    static <K, V> EconomicMap<K, V> create(Equivalence strategy, int initialCapacity) {
        return EconomicMapImpl.create(strategy, initialCapacity, false);
    }

    
Wraps an existing Map as an EconomicMap. 
Since:19.0
/**
     * Wraps an existing {@link Map} as an {@link EconomicMap}.
     *
     * @since 19.0
     */
    static <K, V> EconomicMap<K, V> wrapMap(Map<K, V> map) {
        return new EconomicMap<K, V>() {

            @Override
            public V get(K key) {
                V result = map.get(key);
                return result;
            }

            @Override
            public V put(K key, V value) {
                V result = map.put(key, value);
                return result;
            }

            @Override
            public V putIfAbsent(K key, V value) {
                V result = map.putIfAbsent(key, value);
                return result;
            }

            @Override
            public int size() {
                int result = map.size();
                return result;
            }

            @Override
            public boolean containsKey(K key) {
                return map.containsKey(key);
            }

            @Override
            public void clear() {
                map.clear();
            }

            @Override
            public V removeKey(K key) {
                V result = map.remove(key);
                return result;
            }

            @Override
            public Iterable<V> getValues() {
                return map.values();
            }

            @Override
            public Iterable<K> getKeys() {
                return map.keySet();
            }

            @Override
            public boolean isEmpty() {
                return map.isEmpty();
            }

            @Override
            public MapCursor<K, V> getEntries() {
                Iterator<java.util.Map.Entry<K, V>> iterator = map.entrySet().iterator();
                return new MapCursor<K, V>() {

                    private Map.Entry<K, V> current;

                    @Override
                    public boolean advance() {
                        boolean result = iterator.hasNext();
                        if (result) {
                            current = iterator.next();
                        }

                        return result;
                    }

                    @Override
                    public K getKey() {
                        return current.getKey();
                    }

                    @Override
                    public V getValue() {
                        return current.getValue();
                    }

                    @Override
                    public void remove() {
                        iterator.remove();
                    }
                };
            }

            @Override
            public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
                map.replaceAll(function);
            }
        };
    }
}