HybridDictionary.cs source code in C# .NET

                        Code:
                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / CompMod / System / Collections / Specialized / HybridDictionary.cs / 1 / HybridDictionary.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

namespace System.Collections.Specialized { 
 
    using System.Collections;
    using System.Globalization; 

    /// 
    ///  
    ///    This data structure implements IDictionary first using a linked list 
    ///    (ListDictionary) and then switching over to use Hashtable when large. This is recommended
    ///    for cases where the number of elements in a dictionary is unknown and might be small. 
    /// 
    ///    It also has a single boolean parameter to allow case-sensitivity that is not affected by
    ///    ambient culture and has been optimized for looking up case-insensitive symbols 
    ///  
    /// 
    [Serializable]
    public class HybridDictionary: IDictionary { 

        // These numbers have been carefully tested to be optimal. Please don't change them 
        // without doing thorough performance testing. 
        private const int CutoverPoint = 9;
        private const int InitialHashtableSize = 13; 
        private const int FixedSizeCutoverPoint = 6;

        // Instance variables. This keeps the HybridDictionary very light-weight when empty
        private ListDictionary list; 
        private Hashtable hashtable;
        private bool caseInsensitive; 
 
        /// 
        ///    [To be supplied.] 
        /// 
        public HybridDictionary() {
        }
 
        /// 
        ///    [To be supplied.] 
        ///  
        public HybridDictionary(int initialSize) : this(initialSize, false) {
        } 

        /// 
        ///    [To be supplied.]
        ///  
        public HybridDictionary(bool caseInsensitive) {
            this.caseInsensitive = caseInsensitive; 
        } 

        ///  
        ///    [To be supplied.]
        /// 
        public HybridDictionary(int initialSize, bool caseInsensitive) {
            this.caseInsensitive = caseInsensitive; 
            if (initialSize >= FixedSizeCutoverPoint) {
                if (caseInsensitive) { 
                    hashtable = new Hashtable(initialSize, StringComparer.OrdinalIgnoreCase); 
                } else {
                    hashtable = new Hashtable(initialSize); 
                }
            }
        }
 
        /// 
        ///    [To be supplied.] 
        ///  
        public object this[object key] {
            get { 
                // 
                // Hashtable supports multiple read, one writer thread safety.
                // Although we never made the same guarantee for HybridDictionary,
                // it is still nice to do the same thing here since we have recommended 
                // HybridDictioary as replacement for Hashtable.
                // 
                //  

                ListDictionary cachedList = list; 
                if (hashtable != null) {
                    return hashtable[key];
                } else if (cachedList != null) {
                    return cachedList[key]; 
                } else {
                    //  
                    // cachedList can be null in too cases: 
                    //   (1) The dictionary is empty, we will return null in this case
                    //   (2) There is writer which is doing ChangeOver. However in that case 
                    //       we should see the change to hashtable as well.
                    //       So it should work just fine.
                    // 
                    // 
                    if (key == null) {
                        throw new ArgumentNullException("key", SR.GetString(SR.ArgumentNull_Key)); 
                    } 
                    return null;
                } 
            }
            set {
                if (hashtable != null) {
                    hashtable[key] = value; 
                }
                else if (list != null) { 
                    if (list.Count >= CutoverPoint - 1) { 
                        ChangeOver();
                        hashtable[key] = value; 
                    } else {
                        list[key] = value;
                    }
                } 
                else {
                    list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); 
                    list[key] = value; 
                }
            } 
        }

        private ListDictionary List {
            get { 
                if (list == null) {
                    list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); 
                } 
                return list;
            } 
        }

        private void ChangeOver() {
            IDictionaryEnumerator en = list.GetEnumerator(); 
            Hashtable newTable;
            if (caseInsensitive) { 
                newTable = new Hashtable(InitialHashtableSize, StringComparer.OrdinalIgnoreCase); 
            } else {
                newTable = new Hashtable(InitialHashtableSize); 
            }
            while (en.MoveNext()) {
                newTable.Add(en.Key, en.Value);
            } 
            // 
            // Keep the order of writing to hashtable and list. 
            // We assume we will see the change in hashtable if list is set to null in 
            // this method in another reader thread.
            //  
            hashtable = newTable;
            list = null;
        }
 
        /// 
        ///    [To be supplied.] 
        ///  
        public int Count {
            get { 
                ListDictionary cachedList = list;
                if (hashtable != null) {
                    return hashtable.Count;
                } else if (cachedList != null) { 
                    return cachedList.Count;
                } else { 
                    return 0; 
                }
            } 
        }

        /// 
        ///    [To be supplied.] 
        /// 
        public ICollection Keys { 
            get { 
                if (hashtable != null) {
                    return hashtable.Keys; 
                } else {
                    return List.Keys;
                }
            } 
        }
 
        ///  
        ///    [To be supplied.]
        ///  
        public bool IsReadOnly {
            get {
                return false;
            } 
        }
 
        ///  
        ///    [To be supplied.]
        ///  
        public bool IsFixedSize {
            get {
                return false;
            } 
        }
 
        ///  
        ///    [To be supplied.]
        ///  
        public bool IsSynchronized {
            get {
                return false;
            } 
        }
 
        ///  
        ///    [To be supplied.]
        ///  
        public object SyncRoot {
            get {
                return this;
            } 
        }
 
        ///  
        ///    [To be supplied.]
        ///  
        public ICollection Values {
            get {
                if (hashtable != null) {
                    return hashtable.Values; 
                } else {
                    return List.Values; 
                } 
            }
        } 

        /// 
        ///    [To be supplied.]
        ///  
        public void Add(object key, object value) {
            if (hashtable != null) { 
                hashtable.Add(key, value); 
            } else {
                if (list == null) { 
                    list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null);
                    list.Add(key, value);
                }
                else { 
                    if (list.Count + 1 >= CutoverPoint) {
                        ChangeOver(); 
                        hashtable.Add(key, value); 
                    } else {
                        list.Add(key, value); 
                    }
                }
            }
        } 

        ///  
        ///    [To be supplied.] 
        /// 
        public void Clear() { 
            if(hashtable != null) {
                Hashtable cachedHashtable = hashtable;
                hashtable = null;
                cachedHashtable.Clear(); 
            }
 
            if( list != null) { 
                ListDictionary cachedList = list;
                list = null; 
                cachedList.Clear();
            }
        }
 
        /// 
        ///    [To be supplied.] 
        ///  
        public bool Contains(object key) {
            ListDictionary cachedList = list; 
            if (hashtable != null) {
                return hashtable.Contains(key);
            } else if (cachedList != null) {
                return cachedList.Contains(key); 
            } else {
                if (key == null) { 
                    throw new ArgumentNullException("key", SR.GetString(SR.ArgumentNull_Key)); 
                }
                return false; 
            }
        }

        ///  
        ///    [To be supplied.]
        ///  
        public void CopyTo(Array array, int index)  { 
            if (hashtable != null) {
                hashtable.CopyTo(array, index); 
            } else {
                List.CopyTo(array, index);
            }
        } 

        ///  
        ///    [To be supplied.] 
        /// 
        public IDictionaryEnumerator GetEnumerator() { 
            if (hashtable != null) {
                return hashtable.GetEnumerator();
            }
            if (list == null) { 
                list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null);
            } 
            return list.GetEnumerator(); 
        }
 
        /// 
        /// [To be supplied.]
        /// 
        IEnumerator IEnumerable.GetEnumerator() { 
            if (hashtable != null) {
                return hashtable.GetEnumerator(); 
            } 
            if (list == null) {
                list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); 
            }
            return list.GetEnumerator();
        }
 
        /// 
        ///    [To be supplied.] 
        ///  
        public void Remove(object key) {
            if (hashtable != null) { 
                hashtable.Remove(key);
            }
            else if (list != null){
                list.Remove(key); 
            }
            else { 
                if (key == null) { 
                    throw new ArgumentNullException("key", SR.GetString(SR.ArgumentNull_Key));
                } 
            }
        }
    }
}
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HybridDictionary.cs source code in C# .NET

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