我读了这段代码：
List<long> userIdList = new List<long>();
但是我跳转到 System.Collections.Generic 中的 List 的定义（使用 VS2012），我发现：
public class List<T> : IList<T>, ICollection<T>, IEnumerable<T>, IList, ICollection, IEnumerable
{
// Summary:
// Initializes a new instance of the System.Collections.Generic.List<T> class
// that is empty and has the default initial capacity.
[TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
public List();
//
// Summary:
// Initializes a new instance of the System.Collections.Generic.List<T> class
// that contains elements copied from the specified collection and has sufficient
// capacity to accommodate the number of elements copied.
//
// Parameters:
// collection:
// The collection whose elements are copied to the new list.
//
// Exceptions:
// System.ArgumentNullException:
// collection is null.
public List(IEnumerable<T> collection);
//
// Summary:
// Initializes a new instance of the System.Collections.Generic.List<T> class
// that is empty and has the specified initial capacity.
//
// Parameters:
// capacity:
// The number of elements that the new list can initially store.
//
// Exceptions:
// System.ArgumentOutOfRangeException:
// capacity is less than 0.
[TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
public List(int capacity);
// Summary:
// Gets or sets the total number of elements the internal data structure can
// hold without resizing.
//
// Returns:
// The number of elements that the System.Collections.Generic.List<T> can contain
// before resizing is required.
//
// Exceptions:
// System.ArgumentOutOfRangeException:
// System.Collections.Generic.List<T>.Capacity is set to a value that is less
// than System.Collections.Generic.List<T>.Count.
//
// System.OutOfMemoryException:
// There is not enough memory available on the system.
public int Capacity { get; set; }
//
// Summary:
// Gets the number of elements actually contained in the System.Collections.Generic.List<T>.
//
// Returns:
// The number of elements actually contained in the System.Collections.Generic.List<T>.
public int Count { get; }
// Summary:
// Gets or sets the element at the specified index.
//
// Parameters:
// index:
// The zero-based index of the element to get or set.
//
// Returns:
// The element at the specified index.
//
// Exceptions:
// System.ArgumentOutOfRangeException:
// index is less than 0.-or-index is equal to or greater than System.Collections.Generic.List<T>.Count.
public T this[int index] { get; set; }
// Summary:
// Adds an object to the end of the System.Collections.Generic.List<T>.
//
// Parameters:
// item:
// The object to be added to the end of the System.Collections.Generic.List<T>.
// The value can be null for reference types.
public void Add(T item);
...
这个类既不是接口也不是抽象类，但它没有任何方法的函数体。我知道 ArrayList 和 LinkedList，但对于 List，我不知道它的实现。
我的问题：
List的实现在哪里？- 如果
List等于ArrayList或其他什么东西，那么为什么 .NET 允许两个等效但名称不同的类？如果List在 .NET 中没有等效的类，那么为什么给它起一个如此模糊的名称？
MSDN 表示：
List 类是 ArrayList 类的泛型等效项。通过使用大小根据需要动态增加的数组，它使用 IList 泛型接口进行实现。
所以，我认为这是一个糟糕的名称...
抽象的，我们需要声明一个具体的List实现才能使用它。 - Sayakiss