Add collection-helpers library.

pkg/collection_helpers/lib/equality.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.
+
+/**
+ * Defines equality relations on collections.
+ */
+library dart.collection_helper.equality;
+
+import "dart:collection";
+
+const int _HASH_MASK = 0x7fffffff;
+
+/**
+ * A generic equality relation on objects.
+ */
+abstract class Equality<E> {
+  const factory Equality() = DefaultEquality;
+
+  /**
+   * Compare two elements for being equal.
+   *
+   * This should be a proper equality relation.
+   */
+  bool equals(E e1, E e2);
+
+  /**
+   * Get a hashcode of an element.
+   *
+   * The hashcode should be compatible with [equals], so that if
+   * `equals(a, b)` then `hash(a) == hash(b)`.
+   */
+  int hash(E e);
+
+  /**
+   * Test whether an object is a valid argument to [equals] and [hash].
+   *
+   * Some implementations may be restricted to only work on specific types
+   * of objects.
+   */
+  bool isValidKey(Object o);
+}
+
+/**
+ * Equality of objects that compares only the natural equality of the objects.
+ *
+ * This equality uses the objects' own [Object.==] and [Object.hashCode] for
+ * the equality.
+ */
+class DefaultEquality implements Equality<Object> {
+  const DefaultEquality();
+  bool equals(Object e1, Object e2) => e1 == e2;
+  int hash(Object e) => e.hashCode;
+  bool isValidKey(Object o) => true;
+}
+
+/**
+ * Equality of objects that compares only the identity of the objects.
+ */
+class IdentityEquality implements Equality<Object> {
+  const IdentityEquality();
+  bool equals(Object e1, Object e2) => identical(e1, e2);
+  int hash(Object e) => identityHashCode(e);
+  bool isValidKey(Object o) => true;
+}
+
+/**
+ * Equality on iterables.
+ *
+ * Two iterables are equal if they have the same elements in the same order.
+ */
+class IterableEquality<E> implements Equality<Iterable<E>> {
+  final Equality<E> _elementEquality;
+  const IterableEquality([Equality<E> elementEquality =
+                              const DefaultEquality()])
+      : _elementEquality = elementEquality;
+
+  bool equals(Iterable<E> elements1, Iterable<E> elements2) {
+    if (identical(elements1, elements2)) return true;
+    if (elements1 == null || elements2 == null) return false;
+    Iterator it1 = elements1.iterator;
+    Iterator it2 = elements2.iterator;
+    while (true) {
+      bool hasNext = it1.moveNext();
+      if (hasNext != it2.moveNext()) return false;
+      if (!hasNext) return true;
+      if (!_elementEquality.equals(it1.current, it2.current)) return false;
+    }
+  }
+
+  int hash(Iterable<E> elements) {
+    // Jenkins's one-at-a-time hash function.
+    int hash = 0;
+    for (E element in elements) {
+      int c = _elementEquality.hash(element);
+      hash = (hash + c) & _HASH_MASK;
+      hash = (hash + (hash << 10)) & _HASH_MASK;
+      hash ^= (hash >> 6);
+    }
+    hash = (hash + (hash << 3)) & _HASH_MASK;
+    hash ^= (hash >> 11);
+    hash = (hash + (hash << 15)) & _HASH_MASK;
+    return hash;
+  }
+
+  bool isValidKey(Object o) => o is Iterable<E>;
+}
+
+/**
+ * Equality on lists.
+ *
+ * Two lists are equal if they have the same length and their elements
+ * at each index are equal.
+ *
+ * This is effectively the same as [IterableEquality] except that it
+ * accesses elements by index instead of through iteration.
+ */
+class ListEquality<E> implements Equality<List<E>> {
+  final Equality<E> _elementEquality;
+  const ListEquality([Equality<E> elementEquality = const DefaultEquality()])
+      : _elementEquality = elementEquality;
+
+  bool equals(List<E> e1, List<E> e2) {
+    if (identical(e1, e2)) return true;
+    if (e1 == null || e2 == null) return false;
+    int length = e1.length;
+    if (length != e2.length) return false;
+    for (int i = 0; i < length; i++) {
+      if (!_elementEquality.equals(e1[i], e2[i])) return false;
+    }
+    return true;
+  }
+
+  int hash(List<E> e) {
+    // Jenkins's one-at-a-time hash function.
+    // This code is almost identical to the one in IterableEquality, except
+    // that it uses indexing instead of iterating to get the elements.
+    int hash = 0;
+    for (int i = 0; i < e.length; i++) {
+      int c = _elementEquality.hash(e[i]);
+      hash = (hash + c) & _HASH_MASK;
+      hash = (hash + (hash << 10)) & _HASH_MASK;
+      hash ^= (hash >> 6);
+    }
+    hash = (hash + (hash << 3)) & _HASH_MASK;
+    hash ^= (hash >> 11);
+    hash = (hash + (hash << 15)) & _HASH_MASK;
+    return hash;
+  }
+
+  bool isValidKey(Object o) => o is List<E>;
+}
+
+/**
+ * Equality of the elements of two iterables without considering order.
+ *
+ * Two iterables are considered equal if they have the same number of elements,
+ * and the elements of one set can be paired with the elements
+ * of the other iterable, so that each pair are equal.
+ */
+class UnorderedIterableEquality<E> implements Equality<Iterable<E>> {
+  final Equality<E> _elementEquality;
+
+  const UnorderedIterableEquality(
+      [Equality<E> elementEquality = const DefaultEquality()])
+      : _elementEquality = elementEquality;
+
+  bool equals(Iterable<E> e1, Iterable<E> e2) {
+    if (identical(e1, e2)) return true;
+    if (e1 == null || e2 == null) return false;
+    HashMap<E, int> counts = new HashMap(
+        equals: _elementEquality.equals,
+        hashCode: _elementEquality.hash,
+        isValidKey: _elementEquality.isValidKey);
+    int length = 0;
+    for (E e in e1) {
+      int count = counts[e];
+      if (count == null) count = 0;
+      counts[e] = count + 1;
+      length++;
+    }
+    for (E e in e2) {
+      int count = counts[e];
+      if (count == null || count == 0) return false;
+      counts[e] = count - 1;
+      length--;
+    }
+    return length == 0;
+  }
+
+  int hash(Iterable<E> e) {
+    int hash = 0;
+    for (E element in e) {
+      int c = _elementEquality.hash(element);
+      hash = (hash + c) & _HASH_MASK;
+    }
+    hash = (hash + (hash << 3)) & _HASH_MASK;
+    hash ^= (hash >> 11);
+    hash = (hash + (hash << 15)) & _HASH_MASK;
+    return hash;
+  }
+
+  bool isValidKey(Object o) => o is Iterable<E>;
+}
+
+/**
+ * Equality of sets.
+ *
+ * Two sets are considered equal if they have the same number of elements,
+ * and the elements of one set can be paired with the elements
+ * of the other set, so that each pair are equal.
+ *
+ * This equality behaves the same as [UnorderedIterableEquality] except that
+ * it expects sets instead of iterables as arguments.
+ */
+class SetEquality<E> extends UnorderedIterableEquality<E>
+                     implements Equality<Set<E>> {
+  const SetEquality(
+      [Equality<E> elementEquality = const DefaultEquality()])
+      : super(elementEquality);
+
+  bool equals(Set<E> e1, Set<E> e2) => super.equals(e1, e2);
+
+  int hash(Set<E> e) => super.hash(e);
+
+  bool isValidKey(Object o) => o is Set<E>;
+}
+
+/**
+ *  Internal class used by [MapEquality].
+ *
+ *  The class represents a map entry as a single object,
+ *  using a combined hashCode and equality of the key and value.
+ */
+class _MapEntry {
+  final MapEquality equality;
+  final key;
+  final value;
+  _MapEntry(this.equality, this.key, this.value);
+
+  int get hashCode =>
+      (3 * equality._keyEquality.hash(key) +
+       7 * equality._valueEquality.hash(value)) & _HASH_MASK;
+
+  bool operator==(Object other) {
+    if (other is! _MapEntry) return false;
+    _MapEntry otherEntry = other;
+    return equality._keyEquality.equals(key, otherEntry.key) &&
+           equality._valueEquality.equals(value, otherEntry.value);
+
+  }
+}
+
+/**
+ * Equality on maps.
+ *
+ * Two maps are equal if they have the same number of entries, and if the
+ * entries of the two maps are pairwise equal on both key and value.
+ */
+class MapEquality<K, V> implements Equality<Map<K, V>> {
+  final Equality<K> _keyEquality;
+  final Equality<V> _valueEquality;
+  const MapEquality({ Equality<K> keys : const DefaultEquality(),
+                      Equality<V> values : const DefaultEquality() })
+      : _keyEquality = keys, _valueEquality = values;
+
+  bool equals(Map<K, V> e1, Map<K, V> e2) {
+    if (identical(e1, e2)) return true;
+    if (e1 == null || e2 == null) return false;
+    int length = e1.length;
+    if (length != e2.length) return false;
+    Map<_MapEntry, int> equalElementCounts = new HashMap();
+    for (K key in e1.keys) {
+      _MapEntry entry = new _MapEntry(this, key, e1[key]);
+      int count = equalElementCounts[entry];
+      if (count == null) count = 0;
+      equalElementCounts[entry] = count + 1;
+    }
+    for (K key in e2.keys) {
+      _MapEntry entry = new _MapEntry(this, key, e2[key]);
+      int count = equalElementCounts[entry];
+      if (count == null || count == 0) return false;
+      equalElementCounts[entry] = count - 1;
+    }
+    return true;
+  }
+
+  int hash(Map<K, V> map) {
+    int hash = 0;
+    for (K key in map.keys) {
+      int keyHash = _keyEquality.hash(key);
+      int valueHash = _valueEquality.hash(map[key]);
+      hash = (hash + 3 * keyHash + 7 * valueHash) & _HASH_MASK;
+    }
+    hash = (hash + (hash << 3)) & _HASH_MASK;
+    hash ^= (hash >> 11);
+    hash = (hash + (hash << 15)) & _HASH_MASK;
+    return hash;
+  }
+
+  bool isValidKey(Object o) => o is Map<K, V>;
+}
+
+/**
+ * Combines several equalities into a single equality.
+ *
+ * Tries each equality in order, using [Equality.isValidKey], and returns
+ * the result of the first equality that applies to the argument or arguments.
+ *
+ * For `equals`, the first equality that matches the first argument is used,
+ * and if the second argument of `equals` is not valid for that equality,
+ * it returns false.
+ *
+ * Because the equalities are tried in order, they should generally work on
+ * disjoint types. Otherwise the multi-equality may give inconsistent results
+ * for `equals(e1, e2)` and `equals(e2, e1)`. This can happen if one equality
+ * considers only `e1` a valid key, and not `e2`, but an equality which is
+ * checked later, allows both.
+ */
+class MultiEquality<E> implements Equality<E> {
+  final Iterable<Equality<E>> _equalities;
+
+  const MultiEquality(Iterable<Equality<E>> equalities)
+      : _equalities = equalities;
+
+  bool equals(E e1, E e2) {
+    for (Equality<E> eq in _equalities) {
+      if (eq.isValidKey(e1)) return eq.isValidKey(e2) && eq.equals(e1, e2);
+    }
+    return false;
+  }
+
+  int hash(E e) {
+    for (Equality<E> eq in _equalities) {
+      if (eq.isValidKey(e)) return eq.hash(e);
+    }
+    return -1;
+  }
+
+  bool isValidKey(Object o) {
+    for (Equality<E> eq in _equalities) {
+      if (eq.isValidKey(o)) return true;
+    }
+    return false;
+  }
+}
+
+/**
+ * Deep equality on collections.
+ *
+ * Recognizes lists, sets, iterables and maps and compares their elements using
+ * deep equality as well.
+ *
+ * Non-iterable/map objects are compared using a configurable base equality.
+ *
+ * Works in one of two modes: ordered or unordered.
+ *
+ * In ordered mode, lists and iterables are required to have equal elements
+ * in the same order. In unordered mode, the order of elements in iterables
+ * and lists are not importan.
+ *
+ * A list is only equal to another list, likewise for sets and maps. All other
+ * iterables are compared as iterables only.
+ */
+class DeepCollectionEquality implements Equality {
+  final Equality _base;
+  final bool _unordered;
+  const DeepCollectionEquality([Equality base = const DefaultEquality()])
+      : _base = base, _unordered = false;
+
+  /**
+   * Creates a deep equality on collections where the order of lists and
+   * iterables are not considered important. That is, lists and iterables are
+   * treated as unordered iterables.
+   */
+  const DeepCollectionEquality.unordered(
+      [Equality base = const DefaultEquality()])
+      : _base = base, _unordered = true;
+
+  bool equals(e1, e2) {
+    if (e1 is Set) {
+      if (e2 is! Set) return false;
+      return new SetEquality(this).equals(e1, e2);
+    }
+    if (e1 is Map) {
+      if (e2 is! Map) return false;
+      return new MapEquality(keys: this, values: this).equals(e1, e2);
+    }
+    if (!_unordered) {
+      if (e1 is List) {
+        if (e2 is! List) return false;
+        return new ListEquality(this).equals(e1, e2);
+      }
+      if (e1 is Iterable) {
+        if (e2 is! Iterable) return false;
+        return new IterableEquality(this).equals(e1, e2);
+      }
+    } else if (e1 is Iterable) {
+      if (e2 is! Iterable) return false;
+      if (e1 is List != e2 is List) return false;
+      return new UnorderedIterableEquality(this).equals(e1, e2);
+    }
+    return _base.equals(e1, e2);
+  }
+
+  int hash(Object o) {
+    if (o is Set) return new SetEquality(this).hash(o);
+    if (o is Map) return new MapEquality(keys: this, values: this).hash(o);
+    if (!_unordered) {
+      if (o is List) return new ListEquality(this).hash(o);
+      if (o is Iterable) return new IterableEquality(this).hash(o);
+    } else if (o is Iterable) {
+      return new UnorderedIterableEquality(this).hash(o);
+    }
+    return _base.hash(o);
+  }
+
+  bool isValidKey(Object o) => o is Iterable || o is Map || _base.isValidKey(o);
+}