src/Lucene.Net.Tests/Support/C5/WeakViewList.cs

/*
 Copyright (c) 2003-2016 Niels Kokholm, Peter Sestoft, and Rasmus Lystrøm
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
*/

using System;
using SCG = System.Collections.Generic;

namespace Lucene.Net.Support.C5
{
    /// <summary>
    /// Characterize the mutual position of some view B (other) relative to view A (this)
    /// </summary>
    enum MutualViewPosition
    {
        /// <summary>
        /// B contains A(this)
        /// </summary>
        Contains,
        /// <summary>
        /// B is containd in A(this), but not vice versa
        /// </summary>
        ContainedIn,
        /// <summary>
        /// A and B does not overlap
        /// </summary>
        NonOverlapping,
        /// <summary>
        /// A and B overlap, but neither is contained in the other
        /// </summary>
        Overlapping
    }

    #region View List Nested class
    /// <summary>
    /// This class is shared between the linked list and array list implementations.
    /// </summary>
    /// <typeparam name="V"></typeparam>
#if FEATURE_SERIALIZABLE
    [Serializable]
#endif
    class WeakViewList<V> where V : class
    {
        Node start;

#if FEATURE_SERIALIZABLE
        [Serializable]
#endif
        internal class Node
        {
            internal WeakReference weakview; internal Node prev, next;
            internal Node(V view) { weakview = new WeakReference(view); }
        }
        internal Node Add(V view)
        {
            Node newNode = new Node(view);
            if (start != null) { start.prev = newNode; newNode.next = start; }
            start = newNode;
            return newNode;
        }
        internal void Remove(Node n)
        {
            if (n == start) { start = start.next; if (start != null) start.prev = null; }
            else { n.prev.next = n.next; if (n.next != null) n.next.prev = n.prev; }
        }
        /// <summary>
        /// Note that it is safe to call views.Remove(view.myWeakReference) if view
        /// is the currently yielded object
        /// </summary>
        /// <returns></returns>
        public SCG.IEnumerator<V> GetEnumerator()
        {
            Node n = start;
            while (n != null)
            {
                //V view = n.weakview.Target as V; //This provokes a bug in the beta1 verifyer
                object o = n.weakview.Target;
                V view = o is V ? (V)o : null;
                if (view == null)
                    Remove(n);
                else
                    yield return view;
                n = n.next;
            }
        }
    }

    #endregion
}