Initial version of a serialization framework

pkg/serialization/lib/src/polyfill_identity_set.dart

+// Copyright (c) 2012, 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.
+
+// TODO(alanknight): Replace with proper identity collection. Issue 4161
+library identity_set;
+
+import 'dart:collection';
+
+// Hash map implementation with open addressing and quadratic probing.
+class IdentityMap<K, V> implements HashMap<K, V> {
+
+  // The [_keys] list contains the keys inserted in the map.
+  // The [_keys] list must be a raw list because it
+  // will contain both elements of type K, and the [_DELETED_KEY] of type
+  // [_DeletedKeySentinel].
+  // The alternative of declaring the [_keys] list as of type Object
+  // does not work, because the HashSetIterator constructor would fail:
+  //  HashSetIterator(HashSet<E> set)
+  //    : _nextValidIndex = -1,
+  //      _entries = set_._backingMap._keys {
+  //    _advance();
+  //  }
+  // With K being type int, for example, it would fail because
+  // List<Object> is not assignable to type List<int> of entries.
+  List _keys;
+
+  // The values inserted in the map. For a filled entry index in this
+  // list, there is always the corresponding key in the [keys_] list
+  // at the same entry index.
+  List<V> _values;
+
+  // The load limit is the number of entries we allow until we double
+  // the size of the lists.
+  int _loadLimit;
+
+  // The current number of entries in the map. Will never be greater
+  // than [_loadLimit].
+  int _numberOfEntries;
+
+  // The current number of deleted entries in the map.
+  int _numberOfDeleted;
+
+  // The sentinel when a key is deleted from the map.
+  static const _DeletedKeySentinel _DELETED_KEY = const _DeletedKeySentinel();
+
+  // The initial capacity of a hash map.
+  static const int _INITIAL_CAPACITY = 8;  // must be power of 2
+
+  IdentityMap() {
+    _numberOfEntries = 0;
+    _numberOfDeleted = 0;
+    _loadLimit = _computeLoadLimit(_INITIAL_CAPACITY);
+    _keys = new List(_INITIAL_CAPACITY);
+    _values = new List<V>(_INITIAL_CAPACITY);
+  }
+
+  factory IdentityMap.from(Map<K, V> other) {
+    Map<K, V> result = new IdentityMap<K, V>();
+    other.forEach((K key, V value) { result[key] = value; });
+    return result;
+  }
+
+  static int _computeLoadLimit(int capacity) {
+    return (capacity * 3) ~/ 4;
+  }
+
+  static int _firstProbe(int hashCode, int length) {
+    return hashCode & (length - 1);
+  }
+
+  static int _nextProbe(int currentProbe, int numberOfProbes, int length) {
+    return (currentProbe + numberOfProbes) & (length - 1);
+  }
+
+  int _probeForAdding(K key) {
+    if (key == null) throw new ArgumentError(null);
+    int hash = _firstProbe(key.hashCode, _keys.length);
+    int numberOfProbes = 1;
+    int initialHash = hash;
+    // insertionIndex points to a slot where a key was deleted.
+    int insertionIndex = -1;
+    while (true) {
+      // [existingKey] can be either of type [K] or [_DeletedKeySentinel].
+      Object existingKey = _keys[hash];
+      if (existingKey == null) {
+        // We are sure the key is not already in the set.
+        // If the current slot is empty and we didn't find any
+        // insertion slot before, return this slot.
+        if (insertionIndex < 0) return hash;
+        // If we did find an insertion slot before, return it.
+        return insertionIndex;
+      } else if (identical(existingKey, key)) {
+        // The key is already in the map. Return its slot.
+        return hash;
+      } else if ((insertionIndex < 0) &&
+                 (identical(existingKey, _DELETED_KEY))) {
+        // The slot contains a deleted element. Because previous calls to this
+        // method may not have had this slot deleted, we must continue iterate
+        // to find if there is a slot with the given key.
+        insertionIndex = hash;
+      }
+
+      // We did not find an insertion slot. Look at the next one.
+      hash = _nextProbe(hash, numberOfProbes++, _keys.length);
+      // _ensureCapacity has guaranteed the following cannot happen.
+      // assert(hash != initialHash);
+    }
+  }
+
+  int _probeForLookup(K key) {
+    if (key == null) throw new ArgumentError(null);
+    int hash = _firstProbe(key.hashCode, _keys.length);
+    int numberOfProbes = 1;
+    int initialHash = hash;
+    while (true) {
+      // [existingKey] can be either of type [K] or [_DeletedKeySentinel].
+      Object existingKey = _keys[hash];
+      // If the slot does not contain anything (in particular, it does not
+      // contain a deleted key), we know the key is not in the map.
+      if (existingKey == null) return -1;
+      // The key is in the map, return its index.
+      if (identical(existingKey, key)) return hash;
+      // Go to the next probe.
+      hash = _nextProbe(hash, numberOfProbes++, _keys.length);
+      // _ensureCapacity has guaranteed the following cannot happen.
+      // assert(hash != initialHash);
+    }
+  }
+
+  void _ensureCapacity() {
+    int newNumberOfEntries = _numberOfEntries + 1;
+    // Test if adding an element will reach the load limit.
+    if (newNumberOfEntries >= _loadLimit) {
+      _grow(_keys.length * 2);
+      return;
+    }
+
+    // Make sure that we don't have poor performance when a map
+    // contains lots of deleted entries: we _grow if
+    // there are more deleted entried than free entries.
+    int capacity = _keys.length;
+    int numberOfFreeOrDeleted = capacity - newNumberOfEntries;
+    int numberOfFree = numberOfFreeOrDeleted - _numberOfDeleted;
+    // assert(numberOfFree > 0);
+    if (_numberOfDeleted > numberOfFree) {
+      _grow(_keys.length);
+    }
+  }
+
+  static bool _isPowerOfTwo(int x) {
+    return ((x & (x - 1)) == 0);
+  }
+
+  void _grow(int newCapacity) {
+    assert(_isPowerOfTwo(newCapacity));
+    int capacity = _keys.length;
+    _loadLimit = _computeLoadLimit(newCapacity);
+    List oldKeys = _keys;
+    List<V> oldValues = _values;
+    _keys = new List(newCapacity);
+    _values = new List<V>(newCapacity);
+    for (int i = 0; i < capacity; i++) {
+      // [key] can be either of type [K] or [_DeletedKeySentinel].
+      Object key = oldKeys[i];
+      // If there is no key, we don't need to deal with the current slot.
+      if (key == null || identical(key, _DELETED_KEY)) {
+        continue;
+      }
+      V value = oldValues[i];
+      // Insert the {key, value} pair in their new slot.
+      int newIndex = _probeForAdding(key);
+      _keys[newIndex] = key;
+      _values[newIndex] = value;
+    }
+    _numberOfDeleted = 0;
+  }
+
+  void clear() {
+    _numberOfEntries = 0;
+    _numberOfDeleted = 0;
+    int length = _keys.length;
+    for (int i = 0; i < length; i++) {
+      _keys[i] = null;
+      _values[i] = null;
+    }
+  }
+
+  void operator []=(K key, V value) {
+    _ensureCapacity();
+    int index = _probeForAdding(key);
+    if ((_keys[index] == null) || (identical(_keys[index], _DELETED_KEY))) {
+      _numberOfEntries++;
+    }
+    _keys[index] = key;
+    _values[index] = value;
+  }
+
+  V operator [](K key) {
+    int index = _probeForLookup(key);
+    if (index < 0) return null;
+    return _values[index];
+  }
+
+  V putIfAbsent(K key, V ifAbsent()) {
+    int index = _probeForLookup(key);
+    if (index >= 0) return _values[index];
+
+    V value = ifAbsent();
+    this[key] = value;
+    return value;
+  }
+
+  V remove(K key) {
+    int index = _probeForLookup(key);
+    if (index >= 0) {
+      _numberOfEntries--;
+      V value = _values[index];
+      _values[index] = null;
+      // Set the key to the sentinel to not break the probing chain.
+      _keys[index] = _DELETED_KEY;
+      _numberOfDeleted++;
+      return value;
+    }
+    return null;
+  }
+
+  bool get isEmpty {
+    return _numberOfEntries == 0;
+  }
+
+  int get length {
+    return _numberOfEntries;
+  }
+
+  void forEach(void f(K key, V value)) {
+    int length = _keys.length;
+    for (int i = 0; i < length; i++) {
+      var key = _keys[i];
+      if ((key != null) && (!identical(key, _DELETED_KEY))) {
+        f(key, _values[i]);
+      }
+    }
+  }
+
+
+  Collection<K> get keys {
+    List<K> list = new List<K>(length);
+    int i = 0;
+    forEach((K key, V value) {
+      list[i++] = key;
+    });
+    return list;
+  }
+
+  Collection<V> get values {
+    List<V> list = new List<V>(length);
+    int i = 0;
+    forEach((K key, V value) {
+      list[i++] = value;
+    });
+    return list;
+  }
+
+  bool containsKey(K key) {
+    return (_probeForLookup(key) != -1);
+  }
+
+  bool containsValue(V value) {
+    int length = _values.length;
+    for (int i = 0; i < length; i++) {
+      var key = _keys[i];
+      if ((key != null) && (!identical(key, _DELETED_KEY))) {
+        if (_values[i] == value) return true;
+      }
+    }
+    return false;
+  }
+
+  String toString() {
+    return Maps.mapToString(this);
+  }
+}
+
+
+/**
+ * A singleton sentinel used to represent when a key is deleted from the map.
+ * We can't use [: const Object() :] as a sentinel because it would end up
+ * canonicalized and then we cannot distinguish the deleted key from the
+ * canonicalized [: Object() :].
+ */
+class _DeletedKeySentinel {
+  const _DeletedKeySentinel();
+}
+
+
+/**
+ * This class represents a pair of two objects, used by LinkedHashMap
+ * to store a {key, value} in a list.
+ */
+class _KeyValuePair<K, V> {
+  _KeyValuePair(this.key, this.value) {}
+
+  final K key;
+  V value;
+}
+