Queue.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / CompMod / System / Collections / Generic / Queue.cs / 1305376 / Queue.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*==============================================================================
** 
** Class: Queue 
**
** Purpose: A circular-array implementation of a generic queue. 
**
** Date: January 28, 2003
**
=============================================================================*/ 
namespace System.Collections.Generic {
    using System; 
    using System.Diagnostics; 
    using System.Diagnostics.CodeAnalysis;
    using System.Security.Permissions; 

    // A simple Queue of generic objects.  Internally it is implemented as a
    // circular buffer, so Enqueue can be O(n).  Dequeue is O(1).
    [DebuggerTypeProxy(typeof(System_QueueDebugView<>))] 
    [DebuggerDisplay("Count = {Count}")]
#if !SILVERLIGHT 
    [Serializable()] 
#endif
    [System.Runtime.InteropServices.ComVisible(false)] 
    public class Queue : IEnumerable,
        System.Collections.ICollection {
        private T[] _array;
        private int _head;       // First valid element in the queue 
        private int _tail;       // Last valid element in the queue
        private int _size;       // Number of elements. 
        private int _version; 
#if !SILVERLIGHT
        [NonSerialized] 
#endif
        private Object _syncRoot;

        private const int _MinimumGrow = 4; 
        private const int _ShrinkThreshold = 32;
        private const int _GrowFactor = 200;  // double each time 
        private const int _DefaultCapacity = 4; 
        static T[]  _emptyArray = new T[0];
 
        // Creates a queue with room for capacity objects. The default initial
        // capacity and grow factor are used.
        /// 
        public Queue() { 
            _array = _emptyArray;
        } 
 
        // Creates a queue with room for capacity objects. The default grow factor
        // is used. 
        //
        /// 
        public Queue(int capacity) {
            if (capacity < 0) 
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.capacity, ExceptionResource.ArgumentOutOfRange_NeedNonNegNumRequired);
 
            _array = new T[capacity]; 
            _head = 0;
            _tail = 0; 
            _size = 0;
        }

        // Fills a Queue with the elements of an ICollection.  Uses the enumerator 
        // to get each of the elements.
        // 
        ///  
        public Queue(IEnumerable collection)
        { 
            if (collection == null)
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.collection);

            _array = new T[_DefaultCapacity]; 
            _size = 0;
            _version = 0; 
 
            using(IEnumerator en = collection.GetEnumerator()) {
                while(en.MoveNext()) { 
                    Enqueue(en.Current);
                }
            }
        } 

 
        ///  
        public int Count {
            get { return _size; } 
        }

        /// 
        bool System.Collections.ICollection.IsSynchronized { 
            get { return false; }
        } 
 
        Object System.Collections.ICollection.SyncRoot {
            get { 
                if( _syncRoot == null) {
                    System.Threading.Interlocked.CompareExchange(ref _syncRoot, new Object(), null);
                }
                return _syncRoot; 
            }
        } 
 
        // Removes all Objects from the queue.
        ///  
        public void Clear() {
            if (_head < _tail)
                Array.Clear(_array, _head, _size);
            else { 
                Array.Clear(_array, _head, _array.Length - _head);
                Array.Clear(_array, 0, _tail); 
            } 

            _head = 0; 
            _tail = 0;
            _size = 0;
            _version++;
        } 

        // CopyTo copies a collection into an Array, starting at a particular 
        // index into the array. 
        //
        ///  
        public void CopyTo(T[] array, int arrayIndex)
        {
            if (array==null) {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array); 
            }
 
            if (arrayIndex < 0 || arrayIndex > array.Length) { 
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.arrayIndex, ExceptionResource.ArgumentOutOfRange_Index);
            } 

            int arrayLen = array.Length;
            if (arrayLen - arrayIndex < _size) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen); 
            }
 
            int numToCopy = (arrayLen - arrayIndex < _size) ? (arrayLen - arrayIndex) : _size; 
            if (numToCopy == 0) return;
 
            int firstPart = (_array.Length - _head < numToCopy) ? _array.Length - _head : numToCopy;
            Array.Copy(_array, _head, array, arrayIndex, firstPart);
            numToCopy -= firstPart;
            if (numToCopy > 0) { 
                Array.Copy(_array, 0, array, arrayIndex+_array.Length - _head, numToCopy);
        } 
        } 

        void System.Collections.ICollection.CopyTo(Array array, int index) 
        {
            if (array == null) {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
            } 

            if (array.Rank != 1) { 
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_RankMultiDimNotSupported); 
            }
 
            if( array.GetLowerBound(0) != 0 ) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_NonZeroLowerBound);
            }
 
            int arrayLen = array.Length;
            if (index < 0 || index > arrayLen) { 
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_Index); 
            }
 
            if (arrayLen - index < _size) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
            }
 
            int numToCopy = (arrayLen-index < _size) ? arrayLen-index : _size;
            if (numToCopy == 0) return; 
 
            try {
            int firstPart = (_array.Length - _head < numToCopy) ? _array.Length - _head : numToCopy; 
            Array.Copy(_array, _head, array, index, firstPart);
            numToCopy -= firstPart;

                if (numToCopy > 0) { 
                Array.Copy(_array, 0, array, index+_array.Length - _head, numToCopy);
                } 
            } 
            catch(ArrayTypeMismatchException) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidArrayType); 
            }
        }

        // Adds item to the tail of the queue. 
        //
        ///  
        public void Enqueue(T item) { 
            if (_size == _array.Length) {
                int newcapacity = (int)((long)_array.Length * (long)_GrowFactor / 100); 
                if (newcapacity < _array.Length + _MinimumGrow) {
                    newcapacity = _array.Length + _MinimumGrow;
                }
                SetCapacity(newcapacity); 
            }
 
            _array[_tail] = item; 
            _tail = (_tail + 1) % _array.Length;
            _size++; 
            _version++;
        }

        // GetEnumerator returns an IEnumerator over this Queue.  This 
        // Enumerator will support removing.
        // 
        ///  
        public Enumerator GetEnumerator()
        { 
            return new Enumerator(this);
        }

        ///  
        /// 
        IEnumerator IEnumerable.GetEnumerator() 
        { 
            return new Enumerator(this);
        } 

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return new Enumerator(this); 
        }
 
        // Removes the object at the head of the queue and returns it. If the queue 
        // is empty, this method simply returns null.
        ///  
        public T Dequeue() {
            if (_size == 0)
                ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EmptyQueue);
 
            T removed = _array[_head];
            _array[_head] = default(T); 
            _head = (_head + 1) % _array.Length; 
            _size--;
            _version++; 
            return removed;
        }

        // Returns the object at the head of the queue. The object remains in the 
        // queue. If the queue is empty, this method throws an
        // InvalidOperationException. 
        ///  
        public T Peek() {
            if (_size == 0) 
                ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EmptyQueue);

            return _array[_head];
        } 

        // Returns true if the queue contains at least one object equal to item. 
        // Equality is determined using item.Equals(). 
        //
        // Exceptions: ArgumentNullException if item == null. 
       /// 
       public bool Contains(T item) {
            int index = _head;
            int count = _size; 

            EqualityComparer c = EqualityComparer.Default; 
            while (count-- > 0) { 
                if (((Object) item) == null) {
                    if (((Object) _array[index]) == null) 
                        return true;
                }
                else if (_array[index] != null && c.Equals(_array[index], item)) {
                    return true; 
                }
                index = (index + 1) % _array.Length; 
            } 

            return false; 
        }

        internal T GetElement(int i)
        { 
            return _array[(_head + i) % _array.Length];
        } 
 
        // Iterates over the objects in the queue, returning an array of the
        // objects in the Queue, or an empty array if the queue is empty. 
        // The order of elements in the array is first in to last in, the same
        // order produced by successive calls to Dequeue.
        /// 
        public T[] ToArray() 
        {
            T[] arr = new T[_size]; 
            if (_size==0) 
                return arr;
 
            if (_head < _tail) {
                Array.Copy(_array, _head, arr, 0, _size);
            } else {
                Array.Copy(_array, _head, arr, 0, _array.Length - _head); 
                Array.Copy(_array, 0, arr, _array.Length - _head, _tail);
            } 
 
            return arr;
        } 


        // PRIVATE Grows or shrinks the buffer to hold capacity objects. Capacity
        // must be >= _size. 
        private void SetCapacity(int capacity) {
            T[] newarray = new T[capacity]; 
            if (_size > 0) { 
                if (_head < _tail) {
                    Array.Copy(_array, _head, newarray, 0, _size); 
                } else {
                    Array.Copy(_array, _head, newarray, 0, _array.Length - _head);
                    Array.Copy(_array, 0, newarray, _array.Length - _head, _tail);
                } 
            }
 
            _array = newarray; 
            _head = 0;
            _tail = (_size == capacity) ? 0 : _size; 
            _version++;
        }

        public void TrimExcess() { 
            int threshold = (int)(((double)_array.Length) * 0.9);
            if( _size < threshold ) { 
                SetCapacity(_size); 
            }
        } 

        // Implements an enumerator for a Queue.  The enumerator uses the
        // internal version number of the list to ensure that no modifications are
        // made to the list while an enumeration is in progress. 
        /// 
#if !SILVERLIGHT 
        [Serializable()] 
#endif
        [SuppressMessage("Microsoft.Performance", "CA1815:OverrideEqualsAndOperatorEqualsOnValueTypes", Justification = "not an expected scenario")] 
        public struct Enumerator : IEnumerator,
            System.Collections.IEnumerator
        {
            private Queue _q; 
            private int _index;   // -1 = not started, -2 = ended/disposed
            private int _version; 
            private T _currentElement; 

            internal Enumerator(Queue q) { 
                _q = q;
                _version = _q._version;
                _index = -1;
                _currentElement = default(T); 
            }
 
            ///  
            public void Dispose()
            { 
                _index = -2;
                _currentElement = default(T);
            }
 
            /// 
            public bool MoveNext() { 
                if (_version != _q._version) ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion); 

                if (_index == -2) 
                    return false;

                _index++;
 
                if (_index == _q._size) {
                    _index = -2; 
                    _currentElement = default(T); 
                    return false;
                } 

                _currentElement = _q.GetElement(_index);
                return true;
            } 

            ///  
            public T Current { 
                get {
                    if (_index < 0) 
                    {
                        if (_index == -1)
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumNotStarted);
                        else 
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumEnded);
                    } 
                    return _currentElement; 
                }
            } 

            Object System.Collections.IEnumerator.Current {
                get {
                    if (_index < 0) 
                    {
                        if (_index == -1) 
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumNotStarted); 
                        else
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumEnded); 
                    }
                    return _currentElement;
                }
            } 

            void System.Collections.IEnumerator.Reset() { 
                if (_version != _q._version) ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion); 
                _index = -1;
                _currentElement = default(T); 
            }
        }
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*==============================================================================
** 
** Class: Queue 
**
** Purpose: A circular-array implementation of a generic queue. 
**
** Date: January 28, 2003
**
=============================================================================*/ 
namespace System.Collections.Generic {
    using System; 
    using System.Diagnostics; 
    using System.Diagnostics.CodeAnalysis;
    using System.Security.Permissions; 

    // A simple Queue of generic objects.  Internally it is implemented as a
    // circular buffer, so Enqueue can be O(n).  Dequeue is O(1).
    [DebuggerTypeProxy(typeof(System_QueueDebugView<>))] 
    [DebuggerDisplay("Count = {Count}")]
#if !SILVERLIGHT 
    [Serializable()] 
#endif
    [System.Runtime.InteropServices.ComVisible(false)] 
    public class Queue : IEnumerable,
        System.Collections.ICollection {
        private T[] _array;
        private int _head;       // First valid element in the queue 
        private int _tail;       // Last valid element in the queue
        private int _size;       // Number of elements. 
        private int _version; 
#if !SILVERLIGHT
        [NonSerialized] 
#endif
        private Object _syncRoot;

        private const int _MinimumGrow = 4; 
        private const int _ShrinkThreshold = 32;
        private const int _GrowFactor = 200;  // double each time 
        private const int _DefaultCapacity = 4; 
        static T[]  _emptyArray = new T[0];
 
        // Creates a queue with room for capacity objects. The default initial
        // capacity and grow factor are used.
        /// 
        public Queue() { 
            _array = _emptyArray;
        } 
 
        // Creates a queue with room for capacity objects. The default grow factor
        // is used. 
        //
        /// 
        public Queue(int capacity) {
            if (capacity < 0) 
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.capacity, ExceptionResource.ArgumentOutOfRange_NeedNonNegNumRequired);
 
            _array = new T[capacity]; 
            _head = 0;
            _tail = 0; 
            _size = 0;
        }

        // Fills a Queue with the elements of an ICollection.  Uses the enumerator 
        // to get each of the elements.
        // 
        ///  
        public Queue(IEnumerable collection)
        { 
            if (collection == null)
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.collection);

            _array = new T[_DefaultCapacity]; 
            _size = 0;
            _version = 0; 
 
            using(IEnumerator en = collection.GetEnumerator()) {
                while(en.MoveNext()) { 
                    Enqueue(en.Current);
                }
            }
        } 

 
        ///  
        public int Count {
            get { return _size; } 
        }

        /// 
        bool System.Collections.ICollection.IsSynchronized { 
            get { return false; }
        } 
 
        Object System.Collections.ICollection.SyncRoot {
            get { 
                if( _syncRoot == null) {
                    System.Threading.Interlocked.CompareExchange(ref _syncRoot, new Object(), null);
                }
                return _syncRoot; 
            }
        } 
 
        // Removes all Objects from the queue.
        ///  
        public void Clear() {
            if (_head < _tail)
                Array.Clear(_array, _head, _size);
            else { 
                Array.Clear(_array, _head, _array.Length - _head);
                Array.Clear(_array, 0, _tail); 
            } 

            _head = 0; 
            _tail = 0;
            _size = 0;
            _version++;
        } 

        // CopyTo copies a collection into an Array, starting at a particular 
        // index into the array. 
        //
        ///  
        public void CopyTo(T[] array, int arrayIndex)
        {
            if (array==null) {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array); 
            }
 
            if (arrayIndex < 0 || arrayIndex > array.Length) { 
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.arrayIndex, ExceptionResource.ArgumentOutOfRange_Index);
            } 

            int arrayLen = array.Length;
            if (arrayLen - arrayIndex < _size) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen); 
            }
 
            int numToCopy = (arrayLen - arrayIndex < _size) ? (arrayLen - arrayIndex) : _size; 
            if (numToCopy == 0) return;
 
            int firstPart = (_array.Length - _head < numToCopy) ? _array.Length - _head : numToCopy;
            Array.Copy(_array, _head, array, arrayIndex, firstPart);
            numToCopy -= firstPart;
            if (numToCopy > 0) { 
                Array.Copy(_array, 0, array, arrayIndex+_array.Length - _head, numToCopy);
        } 
        } 

        void System.Collections.ICollection.CopyTo(Array array, int index) 
        {
            if (array == null) {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
            } 

            if (array.Rank != 1) { 
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_RankMultiDimNotSupported); 
            }
 
            if( array.GetLowerBound(0) != 0 ) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_NonZeroLowerBound);
            }
 
            int arrayLen = array.Length;
            if (index < 0 || index > arrayLen) { 
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_Index); 
            }
 
            if (arrayLen - index < _size) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
            }
 
            int numToCopy = (arrayLen-index < _size) ? arrayLen-index : _size;
            if (numToCopy == 0) return; 
 
            try {
            int firstPart = (_array.Length - _head < numToCopy) ? _array.Length - _head : numToCopy; 
            Array.Copy(_array, _head, array, index, firstPart);
            numToCopy -= firstPart;

                if (numToCopy > 0) { 
                Array.Copy(_array, 0, array, index+_array.Length - _head, numToCopy);
                } 
            } 
            catch(ArrayTypeMismatchException) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidArrayType); 
            }
        }

        // Adds item to the tail of the queue. 
        //
        ///  
        public void Enqueue(T item) { 
            if (_size == _array.Length) {
                int newcapacity = (int)((long)_array.Length * (long)_GrowFactor / 100); 
                if (newcapacity < _array.Length + _MinimumGrow) {
                    newcapacity = _array.Length + _MinimumGrow;
                }
                SetCapacity(newcapacity); 
            }
 
            _array[_tail] = item; 
            _tail = (_tail + 1) % _array.Length;
            _size++; 
            _version++;
        }

        // GetEnumerator returns an IEnumerator over this Queue.  This 
        // Enumerator will support removing.
        // 
        ///  
        public Enumerator GetEnumerator()
        { 
            return new Enumerator(this);
        }

        ///  
        /// 
        IEnumerator IEnumerable.GetEnumerator() 
        { 
            return new Enumerator(this);
        } 

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return new Enumerator(this); 
        }
 
        // Removes the object at the head of the queue and returns it. If the queue 
        // is empty, this method simply returns null.
        ///  
        public T Dequeue() {
            if (_size == 0)
                ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EmptyQueue);
 
            T removed = _array[_head];
            _array[_head] = default(T); 
            _head = (_head + 1) % _array.Length; 
            _size--;
            _version++; 
            return removed;
        }

        // Returns the object at the head of the queue. The object remains in the 
        // queue. If the queue is empty, this method throws an
        // InvalidOperationException. 
        ///  
        public T Peek() {
            if (_size == 0) 
                ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EmptyQueue);

            return _array[_head];
        } 

        // Returns true if the queue contains at least one object equal to item. 
        // Equality is determined using item.Equals(). 
        //
        // Exceptions: ArgumentNullException if item == null. 
       /// 
       public bool Contains(T item) {
            int index = _head;
            int count = _size; 

            EqualityComparer c = EqualityComparer.Default; 
            while (count-- > 0) { 
                if (((Object) item) == null) {
                    if (((Object) _array[index]) == null) 
                        return true;
                }
                else if (_array[index] != null && c.Equals(_array[index], item)) {
                    return true; 
                }
                index = (index + 1) % _array.Length; 
            } 

            return false; 
        }

        internal T GetElement(int i)
        { 
            return _array[(_head + i) % _array.Length];
        } 
 
        // Iterates over the objects in the queue, returning an array of the
        // objects in the Queue, or an empty array if the queue is empty. 
        // The order of elements in the array is first in to last in, the same
        // order produced by successive calls to Dequeue.
        /// 
        public T[] ToArray() 
        {
            T[] arr = new T[_size]; 
            if (_size==0) 
                return arr;
 
            if (_head < _tail) {
                Array.Copy(_array, _head, arr, 0, _size);
            } else {
                Array.Copy(_array, _head, arr, 0, _array.Length - _head); 
                Array.Copy(_array, 0, arr, _array.Length - _head, _tail);
            } 
 
            return arr;
        } 


        // PRIVATE Grows or shrinks the buffer to hold capacity objects. Capacity
        // must be >= _size. 
        private void SetCapacity(int capacity) {
            T[] newarray = new T[capacity]; 
            if (_size > 0) { 
                if (_head < _tail) {
                    Array.Copy(_array, _head, newarray, 0, _size); 
                } else {
                    Array.Copy(_array, _head, newarray, 0, _array.Length - _head);
                    Array.Copy(_array, 0, newarray, _array.Length - _head, _tail);
                } 
            }
 
            _array = newarray; 
            _head = 0;
            _tail = (_size == capacity) ? 0 : _size; 
            _version++;
        }

        public void TrimExcess() { 
            int threshold = (int)(((double)_array.Length) * 0.9);
            if( _size < threshold ) { 
                SetCapacity(_size); 
            }
        } 

        // Implements an enumerator for a Queue.  The enumerator uses the
        // internal version number of the list to ensure that no modifications are
        // made to the list while an enumeration is in progress. 
        /// 
#if !SILVERLIGHT 
        [Serializable()] 
#endif
        [SuppressMessage("Microsoft.Performance", "CA1815:OverrideEqualsAndOperatorEqualsOnValueTypes", Justification = "not an expected scenario")] 
        public struct Enumerator : IEnumerator,
            System.Collections.IEnumerator
        {
            private Queue _q; 
            private int _index;   // -1 = not started, -2 = ended/disposed
            private int _version; 
            private T _currentElement; 

            internal Enumerator(Queue q) { 
                _q = q;
                _version = _q._version;
                _index = -1;
                _currentElement = default(T); 
            }
 
            ///  
            public void Dispose()
            { 
                _index = -2;
                _currentElement = default(T);
            }
 
            /// 
            public bool MoveNext() { 
                if (_version != _q._version) ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion); 

                if (_index == -2) 
                    return false;

                _index++;
 
                if (_index == _q._size) {
                    _index = -2; 
                    _currentElement = default(T); 
                    return false;
                } 

                _currentElement = _q.GetElement(_index);
                return true;
            } 

            ///  
            public T Current { 
                get {
                    if (_index < 0) 
                    {
                        if (_index == -1)
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumNotStarted);
                        else 
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumEnded);
                    } 
                    return _currentElement; 
                }
            } 

            Object System.Collections.IEnumerator.Current {
                get {
                    if (_index < 0) 
                    {
                        if (_index == -1) 
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumNotStarted); 
                        else
                            ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumEnded); 
                    }
                    return _currentElement;
                }
            } 

            void System.Collections.IEnumerator.Reset() { 
                if (_version != _q._version) ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion); 
                _index = -1;
                _currentElement = default(T); 
            }
        }
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

                        

                        

                        
                        
                    
                    

                        
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