List泛型

.Net自从2.0以后开始支持泛型。

泛型的作用：可以创建独立于被包含类型的类和方法。泛型类使用泛型类型，并可以根据需要使用特定的类型替换泛型类型。这就保证了类型安全性：如果某个类型不支持泛型类，编译器就会出现错误。

不多说，先记录一下源码：

 // ==++==
 //
 //   Copyright (c) Microsoft Corporation.  All rights reserved.
 //
 // ==--==
 /*============================================================
 **
 ** Class:  List
 **
 ** <OWNER>Microsoft</OWNER>
 **
 ** Purpose: Implements a generic, dynamically sized list as an
 **          array.
 **
 **
 ===========================================================*/
 namespace System.Collections.Generic {
 
     using System;
     using System.Runtime;
     using System.Runtime.Versioning;
     using System.Diagnostics;
     using System.Diagnostics.Contracts;
     using System.Collections.ObjectModel;
     using System.Security.Permissions;
 
     // Implements a variable-size List that uses an array of objects to store the
     // elements. A List has a capacity, which is the allocated length
     // of the internal array. As elements are added to a List, the capacity
     // of the List is automatically increased as required by reallocating the
     // internal array.
     //
     [DebuggerTypeProxy(typeof(Mscorlib_CollectionDebugView<>))]
     [DebuggerDisplay("Count = {Count}")]
     [Serializable]
     public class List<T> : IList<T>, System.Collections.IList, IReadOnlyList<T>
     {
         private const int _defaultCapacity = ;
 
         private T[] _items;
         [ContractPublicPropertyName("Count")]
         private int _size;
         private int _version;
         [NonSerialized]
         private Object _syncRoot;
 
         static readonly T[]  _emptyArray = new T[];        
 
         // Constructs a List. The list is initially empty and has a capacity
         // of zero. Upon adding the first element to the list the capacity is
         // increased to 16, and then increased in multiples of two as required.
         public List() {
             _items = _emptyArray;
         }
 
         // Constructs a List with a given initial capacity. The list is
         // initially empty, but will have room for the given number of elements
         // before any reallocations are required.
         //
         public List(int capacity) {
             if (capacity < ) ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.capacity, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             Contract.EndContractBlock();
 
             if (capacity == )
                 _items = _emptyArray;
             else
                 _items = new T[capacity];
         }
 
         // Constructs a List, copying the contents of the given collection. The
         // size and capacity of the new list will both be equal to the size of the
         // given collection.
         //
         public List(IEnumerable<T> collection) {
             if (collection==null)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.collection);
             Contract.EndContractBlock();
 
             ICollection<T> c = collection as ICollection<T>;
             if( c != null) {
                 int count = c.Count;
                 if (count == )
                 {
                     _items = _emptyArray;
                 }
                 else {
                     _items = new T[count];
                     c.CopyTo(_items, );
                     _size = count;
                 }
             }
             else {
                 _size = ;
                 _items = _emptyArray;
                 // This enumerable could be empty.  Let Add allocate a new array, if needed.
                 // Note it will also go to _defaultCapacity first, not 1, then 2, etc.
 
                 using(IEnumerator<T> en = collection.GetEnumerator()) {
                     while(en.MoveNext()) {
                         Add(en.Current);
                     }
                 }
             }
         }
 
         // Gets and sets the capacity of this list.  The capacity is the size of
         // the internal array used to hold items.  When set, the internal
         // array of the list is reallocated to the given capacity.
         //
         public int Capacity {
             get {
                 Contract.Ensures(Contract.Result<int>() >= );
                 return _items.Length;
             }
             set {
                 if (value < _size) {
                     ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.value, ExceptionResource.ArgumentOutOfRange_SmallCapacity);
                 }
                 Contract.EndContractBlock();
 
                 if (value != _items.Length) {
                     if (value > ) {
                         T[] newItems = new T[value];
                         if (_size > ) {
                             Array.Copy(_items, , newItems, , _size);
                         }
                         _items = newItems;
                     }
                     else {
                         _items = _emptyArray;
                     }
                 }
             }
         }
 
         // Read-only property describing how many elements are in the List.
         public int Count {
             get {
                 Contract.Ensures(Contract.Result<int>() >= );
                 return _size;
             }
         }
 
         bool System.Collections.IList.IsFixedSize {
             get { return false; }
         }
 
         // Is this List read-only?
         bool ICollection<T>.IsReadOnly {
             get { return false; }
         }
 
         bool System.Collections.IList.IsReadOnly {
             get { return false; }
         }
 
         // Is this List synchronized (thread-safe)?
         bool System.Collections.ICollection.IsSynchronized {
             get { return false; }
         }
 
         // Synchronization root for this object.
         Object System.Collections.ICollection.SyncRoot {
             get {
                 if( _syncRoot == null) {
                     System.Threading.Interlocked.CompareExchange<Object>(ref _syncRoot, new Object(), null);
                 }
                 return _syncRoot;
             }
         }
         // Sets or Gets the element at the given index.
         //
         public T this[int index] {
             get {
                 // Following trick can reduce the range check by one
                 if ((uint) index >= (uint)_size) {
                     ThrowHelper.ThrowArgumentOutOfRangeException();
                 }
                 Contract.EndContractBlock();
                 return _items[index];
             }
 
             set {
                 if ((uint) index >= (uint)_size) {
                     ThrowHelper.ThrowArgumentOutOfRangeException();
                 }
                 Contract.EndContractBlock();
                 _items[index] = value;
                 _version++;
             }
         }
 
         private static bool IsCompatibleObject(object value) {
             // Non-null values are fine.  Only accept nulls if T is a class or Nullable<U>.
             // Note that default(T) is not equal to null for value types except when T is Nullable<U>.
             return ((value is T) || (value == null && default(T) == null));
         }
 
         Object System.Collections.IList.this[int index] {
             get {
                 return this[index];
             }
             set {
                 ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(value, ExceptionArgument.value);
 
                 try {
                     this[index] = (T)value;
                 }
                 catch (InvalidCastException) {
                     ThrowHelper.ThrowWrongValueTypeArgumentException(value, typeof(T));
                 }
             }
         }
 
         // Adds the given object to the end of this list. The size of the list is
         // increased by one. If required, the capacity of the list is doubled
         // before adding the new element.
         //
         public void Add(T item) {
             if (_size == _items.Length) EnsureCapacity(_size + );
             _items[_size++] = item;
             _version++;
         }
 
         int System.Collections.IList.Add(Object item)
         {
             ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(item, ExceptionArgument.item);
 
             try {
                 Add((T) item);
             }
             catch (InvalidCastException) {
                 ThrowHelper.ThrowWrongValueTypeArgumentException(item, typeof(T));
             }
 
             return Count - ;
         }
 
         // Adds the elements of the given collection to the end of this list. If
         // required, the capacity of the list is increased to twice the previous
         // capacity or the new size, whichever is larger.
         //
         public void AddRange(IEnumerable<T> collection) {
             Contract.Ensures(Count >= Contract.OldValue(Count));
 
             InsertRange(_size, collection);
         }
 
         public ReadOnlyCollection<T> AsReadOnly() {
             Contract.Ensures(Contract.Result<ReadOnlyCollection<T>>() != null);
             return new ReadOnlyCollection<T>(this);
         }
 
         // Searches a section of the list for a given element using a binary search
         // algorithm. Elements of the list are compared to the search value using
         // the given IComparer interface. If comparer is null, elements of
         // the list are compared to the search value using the IComparable
         // interface, which in that case must be implemented by all elements of the
         // list and the given search value. This method assumes that the given
         // section of the list is already sorted; if this is not the case, the
         // result will be incorrect.
         //
         // The method returns the index of the given value in the list. If the
         // list does not contain the given value, the method returns a negative
         // integer. The bitwise complement operator (~) can be applied to a
         // negative result to produce the index of the first element (if any) that
         // is larger than the given search value. This is also the index at which
         // the search value should be inserted into the list in order for the list
         // to remain sorted.
         //
         // The method uses the Array.BinarySearch method to perform the
         // search.
         //
         public int BinarySearch(int index, int count, T item, IComparer<T> comparer) {
             if (index < )
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             if (count < )
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             if (_size - index < count)
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
             Contract.Ensures(Contract.Result<int>() <= index + count);
             Contract.EndContractBlock();
 
             return Array.BinarySearch<T>(_items, index, count, item, comparer);
         }
 
         public int BinarySearch(T item)
         {
             Contract.Ensures(Contract.Result<int>() <= Count);
             return BinarySearch(, Count, item, null);
         }
 
         public int BinarySearch(T item, IComparer<T> comparer)
         {
             Contract.Ensures(Contract.Result<int>() <= Count);
             return BinarySearch(, Count, item, comparer);
         }
 
         // Clears the contents of List.
         public void Clear() {
             if (_size > )
             {
                 Array.Clear(_items, , _size); // Don't need to doc this but we clear the elements so that the gc can reclaim the references.
                 _size = ;
             }
             _version++;
         }
 
         // Contains returns true if the specified element is in the List.
         // It does a linear, O(n) search.  Equality is determined by calling
         // item.Equals().
         //
         public bool Contains(T item) {
             if ((Object) item == null) {
                 for(int i=; i<_size; i++)
                     if ((Object) _items[i] == null)
                         return true;
                 return false;
             }
             else {
                 EqualityComparer<T> c = EqualityComparer<T>.Default;
                 for(int i=; i<_size; i++) {
                     if (c.Equals(_items[i], item)) return true;
                 }
                 return false;
             }
         }
 
         bool System.Collections.IList.Contains(Object item)
         {
             if(IsCompatibleObject(item)) {
                 return Contains((T) item);
             }
             return false;
         }
 
         public List<TOutput> ConvertAll<TOutput>(Converter<T,TOutput> converter) {
             if( converter == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.converter);
             }
             // @
 
             Contract.EndContractBlock();
 
             List<TOutput> list = new List<TOutput>(_size);
             for( int i = ; i< _size; i++) {
                 list._items[i] = converter(_items[i]);
             }
             list._size = _size;
             return list;
         }
 
         // Copies this List into array, which must be of a
         // compatible array type.
         //
         public void CopyTo(T[] array) {
             CopyTo(array, );
         }
 
         // Copies this List into array, which must be of a
         // compatible array type.
         //
         void System.Collections.ICollection.CopyTo(Array array, int arrayIndex) {
             if ((array != null) && (array.Rank != )) {
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_RankMultiDimNotSupported);
             }
             Contract.EndContractBlock();
 
             try {
                 // Array.Copy will check for NULL.
                 Array.Copy(_items, , array, arrayIndex, _size);
             }
             catch(ArrayTypeMismatchException){
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidArrayType);
             }
         }
 
         // Copies a section of this list to the given array at the given index.
         //
         // The method uses the Array.Copy method to copy the elements.
         //
         public void CopyTo(int index, T[] array, int arrayIndex, int count) {
             if (_size - index < count) {
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
             }
             Contract.EndContractBlock();
 
             // Delegate rest of error checking to Array.Copy.
             Array.Copy(_items, index, array, arrayIndex, count);
         }
 
         public void CopyTo(T[] array, int arrayIndex) {
             // Delegate rest of error checking to Array.Copy.
             Array.Copy(_items, , array, arrayIndex, _size);
         }
 
         // Ensures that the capacity of this list is at least the given minimum
         // value. If the currect capacity of the list is less than min, the
         // capacity is increased to twice the current capacity or to min,
         // whichever is larger.
         private void EnsureCapacity(int min) {
             if (_items.Length < min) {
                 int newCapacity = _items.Length == ? _defaultCapacity : _items.Length * ;
                 // Allow the list to grow to maximum possible capacity (~2G elements) before encountering overflow.
                 // Note that this check works even when _items.Length overflowed thanks to the (uint) cast
                 if ((uint)newCapacity > Array.MaxArrayLength) newCapacity = Array.MaxArrayLength;
                 if (newCapacity < min) newCapacity = min;
                 Capacity = newCapacity;
             }
         }
 
         public bool Exists(Predicate<T> match) {
             return FindIndex(match) != -;
         }
 
         public T Find(Predicate<T> match) {
             if( match == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.EndContractBlock();
 
             for(int i =  ; i < _size; i++) {
                 if(match(_items[i])) {
                     return _items[i];
                 }
             }
             return default(T);
         }
 
         public List<T> FindAll(Predicate<T> match) {
             if( match == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.EndContractBlock();
 
             List<T> list = new List<T>();
             for(int i =  ; i < _size; i++) {
                 if(match(_items[i])) {
                     list.Add(_items[i]);
                 }
             }
             return list;
         }
 
         public int FindIndex(Predicate<T> match) {
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < Count);
             return FindIndex(, _size, match);
         }
 
         public int FindIndex(int startIndex, Predicate<T> match) {
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < startIndex + Count);
             return FindIndex(startIndex, _size - startIndex, match);
         }
 
         public int FindIndex(int startIndex, int count, Predicate<T> match) {
             if( (uint)startIndex > (uint)_size ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.startIndex, ExceptionResource.ArgumentOutOfRange_Index);
             }
 
             if (count <  || startIndex > _size - count) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_Count);
             }
 
             if( match == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < startIndex + count);
             Contract.EndContractBlock();
 
             int endIndex = startIndex + count;
             for( int i = startIndex; i < endIndex; i++) {
                 if( match(_items[i])) return i;
             }
             return -;
         }
 
         public T FindLast(Predicate<T> match) {
             if( match == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.EndContractBlock();
 
             for(int i = _size -  ; i >= ; i--) {
                 if(match(_items[i])) {
                     return _items[i];
                 }
             }
             return default(T);
         }
 
         public int FindLastIndex(Predicate<T> match) {
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < Count);
             return FindLastIndex(_size - , _size, match);
         }
 
         public int FindLastIndex(int startIndex, Predicate<T> match) {
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() <= startIndex);
             return FindLastIndex(startIndex, startIndex + , match);
         }
 
         public int FindLastIndex(int startIndex, int count, Predicate<T> match) {
             if( match == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() <= startIndex);
             Contract.EndContractBlock();
 
             if(_size == ) {
                 // Special case for 0 length List
                 if( startIndex != -) {
                     ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.startIndex, ExceptionResource.ArgumentOutOfRange_Index);
                 }
             }
             else {
                 // Make sure we're not out of range
                 if ( (uint)startIndex >= (uint)_size) {
                     ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.startIndex, ExceptionResource.ArgumentOutOfRange_Index);
                 }
             }
 
             // 2nd have of this also catches when startIndex == MAXINT, so MAXINT - 0 + 1 == -1, which is < 0.
             if (count <  || startIndex - count +  < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_Count);
             }
 
             int endIndex = startIndex - count;
             for( int i = startIndex; i > endIndex; i--) {
                 if( match(_items[i])) {
                     return i;
                 }
             }
             return -;
         }
 
         public void ForEach(Action<T> action) {
             if( action == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.EndContractBlock();
 
             int version = _version;
 
             for(int i =  ; i < _size; i++) {
                 if (version != _version && BinaryCompatibility.TargetsAtLeast_Desktop_V4_5) {
                     break;
                 }
                 action(_items[i]);
             }
 
             if (version != _version && BinaryCompatibility.TargetsAtLeast_Desktop_V4_5)
                 ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion);
         }
 
         // Returns an enumerator for this list with the given
         // permission for removal of elements. If modifications made to the list
         // while an enumeration is in progress, the MoveNext and
         // GetObject methods of the enumerator will throw an exception.
         //
         public Enumerator GetEnumerator() {
             return new Enumerator(this);
         }
 
         /// <internalonly/>
         IEnumerator<T> IEnumerable<T>.GetEnumerator() {
             return new Enumerator(this);
         }
 
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
             return new Enumerator(this);
         }
 
         public List<T> GetRange(int index, int count) {
             if (index < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (count < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (_size - index < count) {
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
             }
             Contract.Ensures(Contract.Result<List<T>>() != null);
             Contract.EndContractBlock();
 
             List<T> list = new List<T>(count);
             Array.Copy(_items, index, list._items, , count);
             list._size = count;
             return list;
         }
 
         // Returns the index of the first occurrence of a given value in a range of
         // this list. The list is searched forwards from beginning to end.
         // The elements of the list are compared to the given value using the
         // Object.Equals method.
         //
         // This method uses the Array.IndexOf method to perform the
         // search.
         //
         public int IndexOf(T item) {
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < Count);
             return Array.IndexOf(_items, item, , _size);
         }
 
         int System.Collections.IList.IndexOf(Object item)
         {
             if(IsCompatibleObject(item)) {
                 return IndexOf((T)item);
             }
             return -;
         }
 
         // Returns the index of the first occurrence of a given value in a range of
         // this list. The list is searched forwards, starting at index
         // index and ending at count number of elements. The
         // elements of the list are compared to the given value using the
         // Object.Equals method.
         //
         // This method uses the Array.IndexOf method to perform the
         // search.
         //
         public int IndexOf(T item, int index) {
             if (index > _size)
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_Index);
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < Count);
             Contract.EndContractBlock();
             return Array.IndexOf(_items, item, index, _size - index);
         }
 
         // Returns the index of the first occurrence of a given value in a range of
         // this list. The list is searched forwards, starting at index
         // index and upto count number of elements. The
         // elements of the list are compared to the given value using the
         // Object.Equals method.
         //
         // This method uses the Array.IndexOf method to perform the
         // search.
         //
         public int IndexOf(T item, int index, int count) {
             if (index > _size)
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_Index);
 
             if (count < || index > _size - count) ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_Count);
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < Count);
             Contract.EndContractBlock();
 
             return Array.IndexOf(_items, item, index, count);
         }
 
         // Inserts an element into this list at a given index. The size of the list
         // is increased by one. If required, the capacity of the list is doubled
         // before inserting the new element.
         //
         public void Insert(int index, T item) {
             // Note that insertions at the end are legal.
             if ((uint) index > (uint)_size) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_ListInsert);
             }
             Contract.EndContractBlock();
             if (_size == _items.Length) EnsureCapacity(_size + );
             if (index < _size) {
                 Array.Copy(_items, index, _items, index + , _size - index);
             }
             _items[index] = item;
             _size++;
             _version++;
         }
 
         void System.Collections.IList.Insert(int index, Object item)
         {
             ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(item, ExceptionArgument.item);
 
             try {
                 Insert(index, (T) item);
             }
             catch (InvalidCastException) {
                 ThrowHelper.ThrowWrongValueTypeArgumentException(item, typeof(T));
             }
         }
 
         // Inserts the elements of the given collection at a given index. If
         // required, the capacity of the list is increased to twice the previous
         // capacity or the new size, whichever is larger.  Ranges may be added
         // to the end of the list by setting index to the List's size.
         //
         public void InsertRange(int index, IEnumerable<T> collection) {
             if (collection==null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.collection);
             }
 
             if ((uint)index > (uint)_size) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_Index);
             }
             Contract.EndContractBlock();
 
             ICollection<T> c = collection as ICollection<T>;
             if( c != null ) {    // if collection is ICollection<T>
                 int count = c.Count;
                 if (count > ) {
                     EnsureCapacity(_size + count);
                     if (index < _size) {
                         Array.Copy(_items, index, _items, index + count, _size - index);
                     }
 
                     // If we're inserting a List into itself, we want to be able to deal with that.
                     if (this == c) {
                         // Copy first part of _items to insert location
                         Array.Copy(_items, , _items, index, index);
                         // Copy last part of _items back to inserted location
                         Array.Copy(_items, index+count, _items, index*, _size-index);
                     }
                     else {
                         T[] itemsToInsert = new T[count];
                         c.CopyTo(itemsToInsert, );
                         itemsToInsert.CopyTo(_items, index);
                     }
                     _size += count;
                 }
             }
             else {
                 using(IEnumerator<T> en = collection.GetEnumerator()) {
                     while(en.MoveNext()) {
                         Insert(index++, en.Current);
                     }
                 }
             }
             _version++;
         }
 
         // Returns the index of the last occurrence of a given value in a range of
         // this list. The list is searched backwards, starting at the end
         // and ending at the first element in the list. The elements of the list
         // are compared to the given value using the Object.Equals method.
         //
         // This method uses the Array.LastIndexOf method to perform the
         // search.
         //
         public int LastIndexOf(T item)
         {
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(Contract.Result<int>() < Count);
             if (_size == ) {  // Special case for empty list
                 return -;
             }
             else {
                 return LastIndexOf(item, _size - , _size);
             }
         }
 
         // Returns the index of the last occurrence of a given value in a range of
         // this list. The list is searched backwards, starting at index
         // index and ending at the first element in the list. The
         // elements of the list are compared to the given value using the
         // Object.Equals method.
         //
         // This method uses the Array.LastIndexOf method to perform the
         // search.
         //
         public int LastIndexOf(T item, int index)
         {
             if (index >= _size)
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_Index);
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(((Count == ) && (Contract.Result<int>() == -)) || ((Count > ) && (Contract.Result<int>() <= index)));
             Contract.EndContractBlock();
             return LastIndexOf(item, index, index + );
         }
 
         // Returns the index of the last occurrence of a given value in a range of
         // this list. The list is searched backwards, starting at index
         // index and upto count elements. The elements of
         // the list are compared to the given value using the Object.Equals
         // method.
         //
         // This method uses the Array.LastIndexOf method to perform the
         // search.
         //
         public int LastIndexOf(T item, int index, int count) {
             if ((Count != ) && (index < )) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if ((Count !=) && (count < )) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
             Contract.Ensures(Contract.Result<int>() >= -);
             Contract.Ensures(((Count == ) && (Contract.Result<int>() == -)) || ((Count > ) && (Contract.Result<int>() <= index)));
             Contract.EndContractBlock();
 
             if (_size == ) {  // Special case for empty list
                 return -;
             }
 
             if (index >= _size) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_BiggerThanCollection);
             }
 
             if (count > index + ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_BiggerThanCollection);
             } 
 
             return Array.LastIndexOf(_items, item, index, count);
         }
 
         // Removes the element at the given index. The size of the list is
         // decreased by one.
         //
         public bool Remove(T item) {
             int index = IndexOf(item);
             if (index >= ) {
                 RemoveAt(index);
                 return true;
             }
 
             return false;
         }
 
         void System.Collections.IList.Remove(Object item)
         {
             if(IsCompatibleObject(item)) {
                 Remove((T) item);
             }
         }
 
         // This method removes all items which matches the predicate.
         // The complexity is O(n).
         public int RemoveAll(Predicate<T> match) {
             if( match == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.Ensures(Contract.Result<int>() >= );
             Contract.Ensures(Contract.Result<int>() <= Contract.OldValue(Count));
             Contract.EndContractBlock();
 
             int freeIndex = ;   // the first free slot in items array
 
             // Find the first item which needs to be removed.
             while( freeIndex < _size && !match(_items[freeIndex])) freeIndex++;
             if( freeIndex >= _size) return ;
 
             int current = freeIndex + ;
             while( current < _size) {
                 // Find the first item which needs to be kept.
                 while( current < _size && match(_items[current])) current++;            
 
                 if( current < _size) {
                     // copy item to the free slot.
                     _items[freeIndex++] = _items[current++];
                 }
             }                       
 
             Array.Clear(_items, freeIndex, _size - freeIndex);
             int result = _size - freeIndex;
             _size = freeIndex;
             _version++;
             return result;
         }
 
         // Removes the element at the given index. The size of the list is
         // decreased by one.
         //
         public void RemoveAt(int index) {
             if ((uint)index >= (uint)_size) {
                 ThrowHelper.ThrowArgumentOutOfRangeException();
             }
             Contract.EndContractBlock();
             _size--;
             if (index < _size) {
                 Array.Copy(_items, index + , _items, index, _size - index);
             }
             _items[_size] = default(T);
             _version++;
         }
 
         // Removes a range of elements from this list.
         //
         public void RemoveRange(int index, int count) {
             if (index < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (count < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (_size - index < count)
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
             Contract.EndContractBlock();
 
             if (count > ) {
                 int i = _size;
                 _size -= count;
                 if (index < _size) {
                     Array.Copy(_items, index + count, _items, index, _size - index);
                 }
                 Array.Clear(_items, _size, count);
                 _version++;
             }
         }
 
         // Reverses the elements in this list.
         public void Reverse() {
             Reverse(, Count);
         }
 
         // Reverses the elements in a range of this list. Following a call to this
         // method, an element in the range given by index and count
         // which was previously located at index i will now be located at
         // index index + (index + count - i - 1).
         //
         // This method uses the Array.Reverse method to reverse the
         // elements.
         //
         public void Reverse(int index, int count) {
             if (index < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (count < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (_size - index < count)
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
             Contract.EndContractBlock();
             Array.Reverse(_items, index, count);
             _version++;
         }
 
         // Sorts the elements in this list.  Uses the default comparer and
         // Array.Sort.
         public void Sort()
         {
             Sort(, Count, null);
         }
 
         // Sorts the elements in this list.  Uses Array.Sort with the
         // provided comparer.
         public void Sort(IComparer<T> comparer)
         {
             Sort(, Count, comparer);
         }
 
         // Sorts the elements in a section of this list. The sort compares the
         // elements to each other using the given IComparer interface. If
         // comparer is null, the elements are compared to each other using
         // the IComparable interface, which in that case must be implemented by all
         // elements of the list.
         //
         // This method uses the Array.Sort method to sort the elements.
         //
         public void Sort(int index, int count, IComparer<T> comparer) {
             if (index < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (count < ) {
                 ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count, ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
             }
 
             if (_size - index < count)
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidOffLen);
             Contract.EndContractBlock();
 
             Array.Sort<T>(_items, index, count, comparer);
             _version++;
         }
 
         public void Sort(Comparison<T> comparison) {
             if( comparison == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.EndContractBlock();
 
             if( _size > ) {
                 IComparer<T> comparer = new Array.FunctorComparer<T>(comparison);
                 Array.Sort(_items, , _size, comparer);
             }
         }
 
         // ToArray returns a new Object array containing the contents of the List.
         // This requires copying the List, which is an O(n) operation.
         public T[] ToArray() {
             Contract.Ensures(Contract.Result<T[]>() != null);
             Contract.Ensures(Contract.Result<T[]>().Length == Count);
 
             T[] array = new T[_size];
             Array.Copy(_items, , array, , _size);
             return array;
         }
 
         // Sets the capacity of this list to the size of the list. This method can
         // be used to minimize a list's memory overhead once it is known that no
         // new elements will be added to the list. To completely clear a list and
         // release all memory referenced by the list, execute the following
         // statements:
         //
         // list.Clear();
         // list.TrimExcess();
         //
         public void TrimExcess() {
             int threshold = (int)(((double)_items.Length) * 0.9);
             if( _size < threshold ) {
                 Capacity = _size;
             }
         }    
 
         public bool TrueForAll(Predicate<T> match) {
             if( match == null) {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
             }
             Contract.EndContractBlock();
 
             for(int i =  ; i < _size; i++) {
                 if( !match(_items[i])) {
                     return false;
                 }
             }
             return true;
         } 
 
         internal static IList<T> Synchronized(List<T> list) {
             return new SynchronizedList(list);
         }
 
         [Serializable()]
         internal class SynchronizedList : IList<T> {
             private List<T> _list;
             private Object _root;
 
             internal SynchronizedList(List<T> list) {
                 _list = list;
                 _root = ((System.Collections.ICollection)list).SyncRoot;
             }
 
             public int Count {
                 get {
                     lock (_root) {
                         return _list.Count;
                     }
                 }
             }
 
             public bool IsReadOnly {
                 get {
                     return ((ICollection<T>)_list).IsReadOnly;
                 }
             }
 
             public void Add(T item) {
                 lock (_root) {
                     _list.Add(item);
                 }
             }
 
             public void Clear() {
                 lock (_root) {
                     _list.Clear();
                 }
             }
 
             public bool Contains(T item) {
                 lock (_root) {
                     return _list.Contains(item);
                 }
             }
 
             public void CopyTo(T[] array, int arrayIndex) {
                 lock (_root) {
                     _list.CopyTo(array, arrayIndex);
                 }
             }
 
             public bool Remove(T item) {
                 lock (_root) {
                     return _list.Remove(item);
                 }
             }
 
             System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
                 lock (_root) {
                     return _list.GetEnumerator();
                 }
             }
 
             IEnumerator<T> IEnumerable<T>.GetEnumerator() {
                 lock (_root) {
                     return ((IEnumerable<T>)_list).GetEnumerator();
                 }
             }
 
             public T this[int index] {
                 get {
                     lock(_root) {
                         return _list[index];
                     }
                 }
                 set {
                     lock(_root) {
                         _list[index] = value;
                     }
                 }
             }
 
             public int IndexOf(T item) {
                 lock (_root) {
                     return _list.IndexOf(item);
                 }
             }
 
             public void Insert(int index, T item) {
                 lock (_root) {
                     _list.Insert(index, item);
                 }
             }
 
             public void RemoveAt(int index) {
                 lock (_root) {
                     _list.RemoveAt(index);
                 }
             }
         }
 
         [Serializable]
         public struct Enumerator : IEnumerator<T>, System.Collections.IEnumerator
         {
             private List<T> list;
             private int index;
             private int version;
             private T current;
 
             internal Enumerator(List<T> list) {
                 this.list = list;
                 index = ;
                 version = list._version;
                 current = default(T);
             }
 
             public void Dispose() {
             }
 
             public bool MoveNext() {
 
                 List<T> localList = list;
 
                 if (version == localList._version && ((uint)index < (uint)localList._size))
                 {
                     current = localList._items[index];
                     index++;
                     return true;
                 }
                 return MoveNextRare();
             }
 
             private bool MoveNextRare()
             {
                 if (version != list._version) {
                     ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion);
                 }
 
                 index = list._size + ;
                 current = default(T);
                 return false;
             }
 
             public T Current {
                 get {
                     return current;
                 }
             }
 
             Object System.Collections.IEnumerator.Current {
                 get {
                     if( index ==  || index == list._size + ) {
                          ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumOpCantHappen);
                     }
                     return Current;
                 }
             }
 
             void System.Collections.IEnumerator.Reset() {
                 if (version != list._version) {
                     ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_EnumFailedVersion);
                 }
 
                 index = ;
                 current = default(T);
             }
 
         }
     }
 }

创建一个Account类

 public class Account
     {
         public string Name { get; private set; }
         public decimal Balance { get; private set; }

         public Account(string name, Decimal balance)
         {
             this.Name = name;
             this.Balance = balance;
         }
     }

创建一个Account类的集合LIst:

 var account = new List<Account>()
             {
                 new Account("Christian",),
                 new Account("Stephanie",),
                 new Account("Angela",),
                 new Account("Matthias",)
             };

跟踪代码可见:

1、通过List类的构造函数创建一个模板类型T（Account）的数组：

 static readonly T[]  _emptyArray = new T[];        

         // Constructs a List. The list is initially empty and has a capacity
         // of zero. Upon adding the first element to the list the capacity is
         // increased to 16, and then increased in multiples of two as required.
         public List() {
             _items = _emptyArray;
         }

2、创建Account 对象（略）

3、调用List类的Add方法。

 public void Add(T item) {
             if (_size == _items.Length) EnsureCapacity(_size + );
             _items[_size++] = item;
             _version++;
         }

 1 // 确保该列表的容量至少是给定的最小值。如果列表的currect容量小于min，容量将增加到当前容量的两倍或最小，无论哪个更大。
 5         private void EnsureCapacity(int min) {
 6             if (_items.Length < min) {
 7                 int newCapacity = _items.Length == 0? _defaultCapacity : _items.Length * 2;//_defaultCapacity =4
 8                 // 允许列表在遇到溢出之前增加到最大容量(~ 2G元素)。
 9                 // Note that this check works even when _items.Length overflowed thanks to the (uint) cast
10                 if ((uint)newCapacity > Array.MaxArrayLength) newCapacity = Array.MaxArrayLength;//Arrat,NaxArrayLength = 2146435071
11                 if (newCapacity < min) newCapacity = min;
12                 Capacity = newCapacity;//=>
13             }
14         }

 public int Capacity {
             get {
                 Contract.Ensures(Contract.Result<int>() >= );
                 return _items.Length;
             }
             set {
                 if (value < _size) {
                     ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.value, ExceptionResource.ArgumentOutOfRange_SmallCapacity);
                 }
                 Contract.EndContractBlock();

                 if (value != _items.Length) {
                     if (value > ) {
                         T[] newItems = new T[value];
                         if (_size > ) {
                             Array.Copy(_items, , newItems, , _size);
                         }
                         _items = newItems;
                     }
                     else {
                         _items = _emptyArray;
                     }
                 }
             }
         }

未多解释，直接上的代码，通过上面的代码可以看出其实List的实现，是同过T[]数组实现的。

还未深掘泛型的实现。研究中。。。