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src/java.base/share/classes/java/util/ImmutableCollections.java

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rev 48550 : 8193128: Reduce number of implementation classes returned by List/Set/Map.of()
8191418: List.of().indexOf(null) doesn't throw NullPointerException
Reviewed-by: smarks, jrose, martin, plevart

*** 70,383 **** static UnsupportedOperationException uoe() { return new UnsupportedOperationException(); } // ---------- List Implementations ---------- ! abstract static class AbstractImmutableList<E> extends AbstractList<E> ! implements RandomAccess, Serializable { @Override public boolean add(E e) { throw uoe(); } @Override public boolean addAll(Collection<? extends E> c) { throw uoe(); } - @Override public boolean addAll(int index, Collection<? extends E> c) { throw uoe(); } @Override public void clear() { throw uoe(); } @Override public boolean remove(Object o) { throw uoe(); } @Override public boolean removeAll(Collection<?> c) { throw uoe(); } @Override public boolean removeIf(Predicate<? super E> filter) { throw uoe(); } - @Override public void replaceAll(UnaryOperator<E> operator) { throw uoe(); } @Override public boolean retainAll(Collection<?> c) { throw uoe(); } - @Override public void sort(Comparator<? super E> c) { throw uoe(); } } ! static final class List0<E> extends AbstractImmutableList<E> { ! private static final List0<?> INSTANCE = new List0<>(); ! @SuppressWarnings("unchecked") ! static <T> List0<T> instance() { ! return (List0<T>) INSTANCE; } ! private List0() { } @Override ! public int size() { ! return 0; } @Override public E get(int index) { ! Objects.checkIndex(index, 0); // always throws IndexOutOfBoundsException ! return null; // but the compiler doesn't know this } ! @Override ! public Iterator<E> iterator() { ! return Collections.emptyIterator(); } ! private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { ! throw new InvalidObjectException("not serial proxy"); } ! private Object writeReplace() { ! return new CollSer(CollSer.IMM_LIST); } ! @Override ! public boolean contains(Object o) { ! Objects.requireNonNull(o); ! return false; } ! @Override ! public boolean containsAll(Collection<?> o) { ! return o.isEmpty(); // implicit nullcheck of o } ! @Override ! public int hashCode() { ! return 1; } } ! static final class List1<E> extends AbstractImmutableList<E> { ! @Stable ! private final E e0; ! List1(E e0) { ! this.e0 = Objects.requireNonNull(e0); } ! @Override ! public int size() { ! return 1; } ! @Override ! public E get(int index) { ! Objects.checkIndex(index, 1); ! return e0; } ! private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { ! throw new InvalidObjectException("not serial proxy"); } ! private Object writeReplace() { ! return new CollSer(CollSer.IMM_LIST, e0); } @Override ! public boolean contains(Object o) { ! return o.equals(e0); // implicit nullcheck of o } @Override ! public int hashCode() { ! return 31 + e0.hashCode(); } } ! static final class List2<E> extends AbstractImmutableList<E> { ! @Stable ! private final E e0; ! @Stable ! private final E e1; ! List2(E e0, E e1) { ! this.e0 = Objects.requireNonNull(e0); ! this.e1 = Objects.requireNonNull(e1); } ! @Override ! public int size() { ! return 2; } ! @Override ! public E get(int index) { ! Objects.checkIndex(index, 2); ! if (index == 0) { ! return e0; ! } else { // index == 1 ! return e1; } } ! @Override ! public boolean contains(Object o) { ! return o.equals(e0) || o.equals(e1); // implicit nullcheck of o } ! @Override ! public int hashCode() { ! int hash = 31 + e0.hashCode(); ! return 31 * hash + e1.hashCode(); } ! private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { ! throw new InvalidObjectException("not serial proxy"); } ! private Object writeReplace() { ! return new CollSer(CollSer.IMM_LIST, e0, e1); } } ! static final class ListN<E> extends AbstractImmutableList<E> { ! @Stable ! private final E[] elements; ! @SafeVarargs ! ListN(E... input) { ! // copy and check manually to avoid TOCTOU ! @SuppressWarnings("unchecked") ! E[] tmp = (E[])new Object[input.length]; // implicit nullcheck of input ! for (int i = 0; i < input.length; i++) { ! tmp[i] = Objects.requireNonNull(input[i]); } - this.elements = tmp; } @Override ! public int size() { ! return elements.length; } @Override ! public E get(int index) { ! Objects.checkIndex(index, elements.length); ! return elements[index]; } @Override ! public boolean contains(Object o) { ! for (E e : elements) { ! if (o.equals(e)) { // implicit nullcheck of o ! return true; } } ! return false; } @Override public int hashCode() { int hash = 1; ! for (E e : elements) { ! hash = 31 * hash + e.hashCode(); } return hash; } ! private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { ! throw new InvalidObjectException("not serial proxy"); } ! private Object writeReplace() { ! return new CollSer(CollSer.IMM_LIST, elements); } } ! // ---------- Set Implementations ---------- ! abstract static class AbstractImmutableSet<E> extends AbstractSet<E> implements Serializable { ! @Override public boolean add(E e) { throw uoe(); } ! @Override public boolean addAll(Collection<? extends E> c) { throw uoe(); } ! @Override public void clear() { throw uoe(); } ! @Override public boolean remove(Object o) { throw uoe(); } ! @Override public boolean removeAll(Collection<?> c) { throw uoe(); } ! @Override public boolean removeIf(Predicate<? super E> filter) { throw uoe(); } ! @Override public boolean retainAll(Collection<?> c) { throw uoe(); } ! } ! static final class Set0<E> extends AbstractImmutableSet<E> { ! private static final Set0<?> INSTANCE = new Set0<>(); ! @SuppressWarnings("unchecked") ! static <T> Set0<T> instance() { ! return (Set0<T>) INSTANCE; } ! private Set0() { } ! ! @Override ! public int size() { ! return 0; } @Override ! public boolean contains(Object o) { ! Objects.requireNonNull(o); ! return false; } @Override ! public boolean containsAll(Collection<?> o) { ! return o.isEmpty(); // implicit nullcheck of o } ! ! @Override ! public Iterator<E> iterator() { ! return Collections.emptyIterator(); } private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { throw new InvalidObjectException("not serial proxy"); } private Object writeReplace() { ! return new CollSer(CollSer.IMM_SET); } - - @Override - public int hashCode() { - return 0; } } ! static final class Set1<E> extends AbstractImmutableSet<E> { @Stable ! private final E e0; ! Set1(E e0) { ! this.e0 = Objects.requireNonNull(e0); } @Override ! public int size() { ! return 1; } @Override ! public boolean contains(Object o) { ! return o.equals(e0); // implicit nullcheck of o } @Override ! public Iterator<E> iterator() { ! return Collections.singletonIterator(e0); } private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { throw new InvalidObjectException("not serial proxy"); } private Object writeReplace() { ! return new CollSer(CollSer.IMM_SET, e0); } - - @Override - public int hashCode() { - return e0.hashCode(); } } ! static final class Set2<E> extends AbstractImmutableSet<E> { @Stable final E e0; @Stable final E e1; ! Set2(E e0, E e1) { if (e0.equals(Objects.requireNonNull(e1))) { // implicit nullcheck of e0 throw new IllegalArgumentException("duplicate element: " + e0); } if (SALT >= 0) { --- 70,505 ---- static UnsupportedOperationException uoe() { return new UnsupportedOperationException(); } // ---------- List Implementations ---------- ! @SuppressWarnings("unchecked") ! static <E> List<E> emptyList() { ! return (List<E>) ListN.EMPTY_LIST; ! } ! ! static abstract class AbstractImmutableCollection<E> extends AbstractCollection<E> { ! // all mutating methods throw UnsupportedOperationException @Override public boolean add(E e) { throw uoe(); } @Override public boolean addAll(Collection<? extends E> c) { throw uoe(); } @Override public void clear() { throw uoe(); } @Override public boolean remove(Object o) { throw uoe(); } @Override public boolean removeAll(Collection<?> c) { throw uoe(); } @Override public boolean removeIf(Predicate<? super E> filter) { throw uoe(); } @Override public boolean retainAll(Collection<?> c) { throw uoe(); } } ! static abstract class AbstractImmutableSet<E> extends AbstractImmutableCollection<E> ! implements Set<E> { ! @Override ! public boolean equals(Object o) { ! if (o == this) { ! return true; ! } else if (!(o instanceof Set)) { ! return false; } ! Collection<?> c = (Collection<?>) o; ! if (c.size() != size()) { ! return false; ! } ! for (Object e : c) { ! if (e == null || !contains(e)) { ! return false; ! } ! } ! return true; ! } @Override ! public abstract int hashCode(); } + static abstract class AbstractImmutableList<E> extends AbstractImmutableCollection<E> + implements List<E>, RandomAccess { + + // all mutating methods throw UnsupportedOperationException + @Override public void add(int index, E element) { throw uoe(); } + @Override public boolean addAll(int index, Collection<? extends E> c) { throw uoe(); } + @Override public E remove(int index) { throw uoe(); } + @Override public void replaceAll(UnaryOperator<E> operator) { throw uoe(); } + @Override public E set(int index, E element) { throw uoe(); } + @Override public void sort(Comparator<? super E> c) { throw uoe(); } + @Override + public List<E> subList(int fromIndex, int toIndex) { + int size = size(); + subListRangeCheck(fromIndex, toIndex, size); + return new SubList<E>(this, fromIndex, toIndex); + } + + private static final class SubList<E> extends AbstractImmutableList<E> + implements RandomAccess { + private final List<E> root; + final int offset; + int size; + + /** + * Constructs a sublist of an arbitrary AbstractList, which is + * not a SubList itself. + */ + SubList(List<E> root, int fromIndex, int toIndex) { + this.root = root; + this.offset = fromIndex; + this.size = toIndex - fromIndex; + } + + /** + * Constructs a sublist of another SubList. + */ + SubList(SubList<E> parent, int fromIndex, int toIndex) { + this.root = parent.root; + this.offset = parent.offset + fromIndex; + this.size = toIndex - fromIndex; + } + public E get(int index) { ! Objects.checkIndex(index, size); ! return root.get(offset + index); } ! public int size() { ! return size; } ! public Iterator<E> iterator() { ! return listIterator(); } ! public ListIterator<E> listIterator(int index) { ! rangeCheck(index); ! ! ListIterator<E> i = root.listIterator(offset + index); ! ! return new ListIterator<>() { ! ! public boolean hasNext() { ! return nextIndex() < size; } ! public E next() { ! if (hasNext()) { ! return i.next(); ! } else { ! throw new NoSuchElementException(); ! } } ! public boolean hasPrevious() { ! return previousIndex() >= 0; } ! public E previous() { ! if (hasPrevious()) { ! return i.previous(); ! } else { ! throw new NoSuchElementException(); } } ! public int nextIndex() { ! return i.nextIndex() - offset; ! } ! public int previousIndex() { ! return i.previousIndex() - offset; } ! public void remove() { throw uoe(); } ! public void set(E e) { throw uoe(); } ! public void add(E e) { throw uoe(); } ! }; } ! public List<E> subList(int fromIndex, int toIndex) { ! subListRangeCheck(fromIndex, toIndex, size); ! return new SubList<>(this, fromIndex, toIndex); } ! private void rangeCheck(int index) { ! if (index < 0 || index > size) { ! throw outOfBounds(index); ! } ! } } ! static void subListRangeCheck(int fromIndex, int toIndex, int size) { ! if (fromIndex < 0) ! throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); ! if (toIndex > size) ! throw new IndexOutOfBoundsException("toIndex = " + toIndex); ! if (fromIndex > toIndex) ! throw new IllegalArgumentException("fromIndex(" + fromIndex + ! ") > toIndex(" + toIndex + ")"); } @Override ! public Iterator<E> iterator() { ! return new Itr(size()); } @Override ! public ListIterator<E> listIterator() { ! return listIterator(0); ! } ! ! @Override ! public ListIterator<E> listIterator(final int index) { ! int size = size(); ! if (index < 0 || index > size) { ! throw outOfBounds(index); } + return new ListItr(index, size); } ! private class Itr implements Iterator<E> { ! int cursor; ! ! private final int size; ! ! Itr(int size) { ! this.size = size; } ! public boolean hasNext() { ! return cursor != size; } ! public E next() { ! try { ! int i = cursor; ! E next = get(i); ! cursor = i + 1; ! return next; ! } catch (IndexOutOfBoundsException e) { ! throw new NoSuchElementException(); } } ! public void remove() { ! throw uoe(); ! } } ! private class ListItr extends Itr implements ListIterator<E> { ! ! ListItr(int index, int size) { ! super(size); ! cursor = index; } ! public boolean hasPrevious() { ! return cursor != 0; } ! public E previous() { ! try { ! int i = cursor - 1; ! E previous = get(i); ! cursor = i; ! return previous; ! } catch (IndexOutOfBoundsException e) { ! throw new NoSuchElementException(); } } ! public int nextIndex() { ! return cursor; ! } ! public int previousIndex() { ! return cursor - 1; ! } ! ! public void set(E e) { ! throw uoe(); ! } ! ! public void add(E e) { ! throw uoe(); } } @Override ! public boolean equals(Object o) { ! if (o == this) { ! return true; ! } ! ! if (!(o instanceof List)) { ! return false; ! } ! ! Iterator<?> oit = ((List<?>) o).iterator(); ! for (int i = 0, s = size(); i < s; i++) { ! if (!oit.hasNext() || !get(i).equals(oit.next())) { ! return false; ! } ! } ! return !oit.hasNext(); } @Override ! public int indexOf(Object o) { ! Objects.requireNonNull(o); ! for (int i = 0, s = size(); i < s; i++) { ! if (o.equals(get(i))) { ! return i; ! } ! } ! return -1; } @Override ! public int lastIndexOf(Object o) { ! Objects.requireNonNull(o); ! for (int i = size() - 1; i >= 0; i--) { ! if (o.equals(get(i))) { ! return i; } } ! return -1; } @Override public int hashCode() { int hash = 1; ! for (int i = 0, s = size(); i < s; i++) { ! hash = 31 * hash + get(i).hashCode(); } return hash; } ! @Override ! public boolean contains(Object o) { ! return indexOf(o) >= 0; } ! IndexOutOfBoundsException outOfBounds(int index) { ! return new IndexOutOfBoundsException("Index: " + index + " Size: " + size()); } } ! static final class List12<E> extends AbstractImmutableList<E> ! implements Serializable { ! @Stable ! private final E e0; ! @Stable ! private final E e1; ! List12(E e0) { ! this.e0 = Objects.requireNonNull(e0); ! this.e1 = null; } ! List12(E e0, E e1) { ! this.e0 = Objects.requireNonNull(e0); ! this.e1 = Objects.requireNonNull(e1); } @Override ! public int size() { ! return e1 != null ? 2 : 1; } @Override ! public E get(int index) { ! if (index == 0) { ! return e0; ! } else if (index == 1 && e1 != null) { ! return e1; } ! throw outOfBounds(index); } private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { throw new InvalidObjectException("not serial proxy"); } private Object writeReplace() { ! if (e1 == null) { ! return new CollSer(CollSer.IMM_LIST, e0); ! } else { ! return new CollSer(CollSer.IMM_LIST, e0, e1); } } + } ! static final class ListN<E> extends AbstractImmutableList<E> ! implements Serializable { ! ! static final List<?> EMPTY_LIST = new ListN<>(); ! @Stable ! private final E[] elements; ! @SafeVarargs ! ListN(E... input) { ! // copy and check manually to avoid TOCTOU ! @SuppressWarnings("unchecked") ! E[] tmp = (E[])new Object[input.length]; // implicit nullcheck of input ! for (int i = 0; i < input.length; i++) { ! tmp[i] = Objects.requireNonNull(input[i]); ! } ! elements = tmp; } @Override ! public boolean isEmpty() { ! return size() == 0; } @Override ! public int size() { ! return elements.length; } @Override ! public E get(int index) { ! return elements[index]; } private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { throw new InvalidObjectException("not serial proxy"); } private Object writeReplace() { ! return new CollSer(CollSer.IMM_LIST, elements); } } + + // ---------- Set Implementations ---------- + + @SuppressWarnings("unchecked") + static <E> Set<E> emptySet() { + return (Set<E>) SetN.EMPTY_SET; } ! static final class Set12<E> extends AbstractImmutableSet<E> ! implements Serializable { ! @Stable final E e0; @Stable final E e1; ! Set12(E e0) { ! this.e0 = Objects.requireNonNull(e0); ! this.e1 = null; ! } ! ! Set12(E e0, E e1) { if (e0.equals(Objects.requireNonNull(e1))) { // implicit nullcheck of e0 throw new IllegalArgumentException("duplicate element: " + e0); } if (SALT >= 0) {
*** 389,428 **** } } @Override public int size() { ! return 2; } @Override public boolean contains(Object o) { return o.equals(e0) || o.equals(e1); // implicit nullcheck of o } @Override public int hashCode() { ! return e0.hashCode() + e1.hashCode(); } @Override public Iterator<E> iterator() { ! return new Iterator<E>() { ! private int idx = 0; @Override public boolean hasNext() { ! return idx < 2; } @Override public E next() { ! if (idx == 0) { ! idx = 1; return e0; ! } else if (idx == 1) { ! idx = 2; return e1; } else { throw new NoSuchElementException(); } } --- 511,550 ---- } } @Override public int size() { ! return (e1 == null) ? 1 : 2; } @Override public boolean contains(Object o) { return o.equals(e0) || o.equals(e1); // implicit nullcheck of o } @Override public int hashCode() { ! return e0.hashCode() + (e1 == null ? 0 : e1.hashCode()); } @Override public Iterator<E> iterator() { ! return new Iterator<>() { ! private int idx = size(); @Override public boolean hasNext() { ! return idx > 0; } @Override public E next() { ! if (idx == 1) { ! idx = 0; return e0; ! } else if (idx == 2) { ! idx = 1; return e1; } else { throw new NoSuchElementException(); } }
*** 432,452 **** private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { throw new InvalidObjectException("not serial proxy"); } private Object writeReplace() { return new CollSer(CollSer.IMM_SET, e0, e1); } } /** * An array-based Set implementation. The element array must be strictly * larger than the size (the number of contained elements) so that at * least one null is always present. * @param <E> the element type */ ! static final class SetN<E> extends AbstractImmutableSet<E> { @Stable final E[] elements; @Stable final int size; --- 554,582 ---- private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { throw new InvalidObjectException("not serial proxy"); } private Object writeReplace() { + if (e1 == null) { + return new CollSer(CollSer.IMM_SET, e0); + } else { return new CollSer(CollSer.IMM_SET, e0, e1); } } + } /** * An array-based Set implementation. The element array must be strictly * larger than the size (the number of contained elements) so that at * least one null is always present. * @param <E> the element type */ ! static final class SetN<E> extends AbstractImmutableSet<E> ! implements Serializable { ! ! static final Set<?> EMPTY_SET = new SetN<>(); ! @Stable final E[] elements; @Stable final int size;
*** 472,487 **** return size; } @Override public boolean contains(Object o) { ! return probe(o) >= 0; // implicit nullcheck of o } @Override public Iterator<E> iterator() { ! return new Iterator<E>() { private int idx = 0; @Override public boolean hasNext() { while (idx < elements.length) { --- 602,618 ---- return size; } @Override public boolean contains(Object o) { ! Objects.requireNonNull(o); ! return size > 0 && probe(o) >= 0; } @Override public Iterator<E> iterator() { ! return new Iterator<>() { private int idx = 0; @Override public boolean hasNext() { while (idx < elements.length) {
*** 547,556 **** --- 678,692 ---- } } // ---------- Map Implementations ---------- + @SuppressWarnings("unchecked") + static <K,V> Map<K,V> emptyMap() { + return (Map<K,V>) MapN.EMPTY_MAP; + } + abstract static class AbstractImmutableMap<K,V> extends AbstractMap<K,V> implements Serializable { @Override public void clear() { throw uoe(); } @Override public V compute(K key, BiFunction<? super K,? super V,? extends V> rf) { throw uoe(); } @Override public V computeIfAbsent(K key, Function<? super K,? extends V> mf) { throw uoe(); } @Override public V computeIfPresent(K key, BiFunction<? super K,? super V,? extends V> rf) { throw uoe(); }
*** 563,613 **** @Override public V replace(K key, V value) { throw uoe(); } @Override public boolean replace(K key, V oldValue, V newValue) { throw uoe(); } @Override public void replaceAll(BiFunction<? super K,? super V,? extends V> f) { throw uoe(); } } - static final class Map0<K,V> extends AbstractImmutableMap<K,V> { - private static final Map0<?,?> INSTANCE = new Map0<>(); - - @SuppressWarnings("unchecked") - static <K,V> Map0<K,V> instance() { - return (Map0<K,V>) INSTANCE; - } - - private Map0() { } - - @Override - public Set<Map.Entry<K,V>> entrySet() { - return Set.of(); - } - - @Override - public boolean containsKey(Object o) { - Objects.requireNonNull(o); - return false; - } - - @Override - public boolean containsValue(Object o) { - Objects.requireNonNull(o); - return false; - } - - private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { - throw new InvalidObjectException("not serial proxy"); - } - - private Object writeReplace() { - return new CollSer(CollSer.IMM_MAP); - } - - @Override - public int hashCode() { - return 0; - } - } - static final class Map1<K,V> extends AbstractImmutableMap<K,V> { @Stable private final K k0; @Stable private final V v0; --- 699,708 ----
*** 654,665 **** --- 749,764 ---- * in the map) so that at least one null key is always present. * @param <K> the key type * @param <V> the value type */ static final class MapN<K,V> extends AbstractImmutableMap<K,V> { + + static final Map<?,?> EMPTY_MAP = new MapN<>(); + @Stable final Object[] table; // pairs of key, value + @Stable final int size; // number of pairs MapN(Object... input) { if ((input.length & 1) != 0) { // implicit nullcheck of input
*** 687,704 **** } } @Override public boolean containsKey(Object o) { ! return probe(o) >= 0; // implicit nullcheck of o } @Override public boolean containsValue(Object o) { for (int i = 1; i < table.length; i += 2) { Object v = table[i]; ! if (v != null && o.equals(v)) { // implicit nullcheck of o return true; } } return false; } --- 786,805 ---- } } @Override public boolean containsKey(Object o) { ! Objects.requireNonNull(o); ! return size > 0 && probe(o) >= 0; } @Override public boolean containsValue(Object o) { + Objects.requireNonNull(o); for (int i = 1; i < table.length; i += 2) { Object v = table[i]; ! if (v != null && o.equals(v)) { return true; } } return false; }
*** 716,725 **** --- 817,830 ---- } @Override @SuppressWarnings("unchecked") public V get(Object o) { + if (size == 0) { + Objects.requireNonNull(o); + return null; + } int i = probe(o); if (i >= 0) { return (V)table[i+1]; } else { return null;
*** 731,749 **** return size; } @Override public Set<Map.Entry<K,V>> entrySet() { ! return new AbstractSet<Map.Entry<K,V>>() { @Override public int size() { return MapN.this.size; } @Override public Iterator<Map.Entry<K,V>> iterator() { ! return new Iterator<Map.Entry<K,V>>() { int idx = 0; @Override public boolean hasNext() { while (idx < table.length) { --- 836,854 ---- return size; } @Override public Set<Map.Entry<K,V>> entrySet() { ! return new AbstractSet<>() { @Override public int size() { return MapN.this.size; } @Override public Iterator<Map.Entry<K,V>> iterator() { ! return new Iterator<>() { int idx = 0; @Override public boolean hasNext() { while (idx < table.length) {
*** 946,956 **** return List.of(array); case IMM_SET: return Set.of(array); case IMM_MAP: if (array.length == 0) { ! return ImmutableCollections.Map0.instance(); } else if (array.length == 2) { return new ImmutableCollections.Map1<>(array[0], array[1]); } else { return new ImmutableCollections.MapN<>(array); } --- 1051,1061 ---- return List.of(array); case IMM_SET: return Set.of(array); case IMM_MAP: if (array.length == 0) { ! return ImmutableCollections.emptyMap(); } else if (array.length == 2) { return new ImmutableCollections.Map1<>(array[0], array[1]); } else { return new ImmutableCollections.MapN<>(array); }
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