Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataEntity / System / Data / Common / Utils / ModifiableIteratorCollection.cs / 1305376 / ModifiableIteratorCollection.cs
//---------------------------------------------------------------------- //// Copyright (c) Microsoft Corporation. All rights reserved. // // // @owner [....] // @backupOwner [....] //--------------------------------------------------------------------- using System; using System.Collections; using System.Collections.Generic; using System.Text; using System.Diagnostics; namespace System.Data.Common.Utils { // A collection abstraction that allows elements to be removed during // iteration without resulting in missed or duplicate elements in the // iteration process. Also, allows the iterator to be restarted // midway. It is recommended that this abstractions be used for small // sets since Contains is an O(n) algorithm // Restriction: There can be at most ONE iterator on the object at any // given time. internal class ModifiableIteratorCollection: InternalBase { #region Constructors // effects: Generates a set based on values internal ModifiableIteratorCollection(IEnumerable elements) { m_elements = new List (elements); m_currentIteratorIndex = -1; } #endregion #region Fields // A constant to denote the fact that iterator is not running currently // The collection is simply a list private List m_elements; // The index where the iterator is currently at private int m_currentIteratorIndex; #endregion #region Properties // effects: Returns true if the collection has no elements internal bool IsEmpty { get { return m_elements.Count == 0; } } #endregion #region Available Methods // requires: IsEmpty is false // effects: Removes some element from this and returns it internal TElement RemoveOneElement() { Debug.Assert(false == IsEmpty, "Empty set - cannot remove any element"); // Remove the last element return Remove(m_elements.Count - 1); } // requires; An iterator is currently under progress // effects: Resets the current iterator so that it starts from the beginning internal void ResetIterator() { m_currentIteratorIndex = -1; // This will be incremented after the yield statement if the // iterator is on } // requires; An iterator is currently under progress // effects: Removes the current element being yielded while Ensuring // that no element is missed or repeated even after removal internal void RemoveCurrentOfIterator() { Debug.Assert(m_currentIteratorIndex >= 0, "Iterator not started yet"); Remove(m_currentIteratorIndex); // We removed an element at m_currentIteratorIndex by placing the // last element at m_currentIteratorIndex. We need to make // sure that this element is not missed. We reduce // m_currentIteratorIndex by 1 so that when it is incremented // in Elements. So this could even set it to -1 m_currentIteratorIndex--; } // requires; An iterator is not currently under progress // effects: Yields the elements in this internal IEnumerable Elements() { // We cannnot check that an iterator is under progress because // the last time around, the caller may have called a "break" in // their foreach // Yield the elements -- any removal method ensures that // m_currentIteratorIndex is set correctly so that the ++ does // the right thing m_currentIteratorIndex = 0; while (m_currentIteratorIndex < m_elements.Count) { yield return m_elements[m_currentIteratorIndex]; m_currentIteratorIndex++; } } internal override void ToCompactString(StringBuilder builder) { StringUtil.ToCommaSeparatedString(builder, m_elements); } #endregion #region Private Methods // requires: The array is at least of size index+1 // effects: Removes the element at index private TElement Remove(int index) { Debug.Assert(index < m_elements.Count, "Removing an entry with too high an index"); // Place the last element at "index" and remove the last element TElement element = m_elements[index]; int lastIndex = m_elements.Count - 1; m_elements[index] = m_elements[lastIndex]; m_elements.RemoveAt(lastIndex); return element; } #endregion } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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