unfork DDC's copy of most SDK libraries

pkg/dev_compiler/tool/input_sdk/lib/collection/hash_set.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-part of dart.collection;
-
-/** Common parts of [HashSet] and [LinkedHashSet] implementations. */
-abstract class _HashSetBase<E> extends SetBase<E> {
-
-  // The following two methods override the ones in SetBase.
-  // It's possible to be more efficient if we have a way to create an empty
-  // set of the correct type.
-
-  Set<E> difference(Set<Object> other) {
-    Set<E> result = _newSet();
-    for (var element in this) {
-      if (!other.contains(element)) result.add(element);
-    }
-    return result;
-  }
-
-  Set<E> intersection(Set<Object> other) {
-    Set<E> result = _newSet();
-    for (var element in this) {
-      if (other.contains(element)) result.add(element);
-    }
-    return result;
-  }
-
-  Set<E> _newSet();
-
-  // Subclasses can optimize this further.
-  Set<E> toSet() => _newSet()..addAll(this);
-}
-
-/**
- * An unordered hash-table based [Set] implementation.
- *
- * The elements of a `HashSet` must have consistent equality
- * and hashCode implementations. This means that the equals operation
- * must define a stable equivalence relation on the elements (reflexive,
- * symmetric, transitive, and consistent over time), and that the hashCode
- * must consistent with equality, so that the same for objects that are
- * considered equal.
- *
- * The set allows `null` as an element.
- *
- * Most simple operations on `HashSet` are done in (potentially amorteized)
- * constant time: [add], [contains], [remove], and [length], provided the hash
- * codes of objects are well distributed.
- */
-abstract class HashSet<E> implements Set<E> {
-  /**
-   * Create a hash set using the provided [equals] as equality.
-   *
-   * The provided [equals] must define a stable equivalence relation, and
-   * [hashCode] must be consistent with [equals]. If the [equals] or [hashCode]
-   * methods won't work on all objects, but only on some instances of E, the
-   * [isValidKey] predicate can be used to restrict the keys that the functions
-   * are applied to.
-   * Any key for which [isValidKey] returns false is automatically assumed
-   * to not be in the set when asking `contains`.
-   *
-   * If [equals] or [hashCode] are omitted, the set uses
-   * the elements' intrinsic [Object.operator==] and [Object.hashCode].
-   *
-   * If you supply one of [equals] and [hashCode],
-   * you should generally also to supply the other.
-   *
-   * If the supplied `equals` or `hashCode` functions won't work on all [E]
-   * objects, and the map will be used in a setting where a non-`E` object
-   * is passed to, e.g., `contains`, then the [isValidKey] function should
-   * also be supplied.
-   *
-   * If [isValidKey] is omitted, it defaults to testing if the object is an
-   * [E] instance. That means that:
-   *
-   *     new HashSet<int>(equals: (int e1, int e2) => (e1 - e2) % 5 == 0,
-   *                      hashCode: (int e) => e % 5)
-   *
-   * does not need an `isValidKey` argument, because it defaults to only
-   * accepting `int` values which are accepted by both `equals` and `hashCode`.
-   *
-   * If neither `equals`, `hashCode`, nor `isValidKey` is provided,
-   * the default `isValidKey` instead accepts all values.
-   * The default equality and hashcode operations are assumed to work on all
-   * objects.
-   *
-   * Likewise, if `equals` is [identical], `hashCode` is [identityHashCode]
-   * and `isValidKey` is omitted, the resulting set is identity based,
-   * and the `isValidKey` defaults to accepting all keys.
-   * Such a map can be created directly using [HashSet.identity].
-   */
-  external factory HashSet({bool equals(E e1, E e2),
-                            int hashCode(E e),
-                            bool isValidKey(Object potentialKey)});
-
-  /**
-   * Creates an unordered identity-based set.
-   *
-   * Effectively a shorthand for:
-   *
-   *     new HashSet<E>(equals: identical,
-   *                    hashCode: identityHashCode)
-   */
-  external factory HashSet.identity();
-
-  /**
-   * Create a hash set containing all [elements].
-   *
-   * Creates a hash set as by `new HashSet<E>()` and adds each element of
-   * `elements` to this set in the order they are iterated.
-   *
-   * All the [elements] should be assignable to [E].
-   * The `elements` iterable itself may have any element type, so this
-   * constructor can be used to down-cast a `Set`, for example as:
-   *
-   *     Set<SuperType> superSet = ...;
-   *     Set<SubType> subSet =
-   *         new HashSet<SubType>.from(superSet.where((e) => e is SubType));
-   */
-  factory HashSet.from(Iterable elements) {
-    HashSet<E> result = new HashSet<E>();
-    for (final e in elements) {
-      E element = e as Object/*=E*/;
-      result.add(element);
-    }
-    return result;
-  }
-
-  /**
-   * Provides an iterator that iterates over the elements of this set.
-   *
-   * The order of iteration is unspecified,
-   * but consistent between changes to the set.
-   */
-  Iterator<E> get iterator;
-}