为什么需要IEnumerable<T>转成List<T>

这其实涉及到C#的两个问题：

1. 引用对象的赋值是不是如你所预期；
2. 为什么需要IEnumerable转成List

不看结果，先看代码：

'''C#
var indexArray = new int[]{1,2,3,4,5,6 };
var members = indexArray.Select (i => new Member{ Index = i });

Console.WriteLine ("Case 1");
var member1 = members.FirstOrDefault (m => m.Index == 1);
var member1_C = member1;
var member1_W = members.FirstOrDefault (m => m.Index == 1);
member1.Name = "Yang SHEN (Case 1)";
Console.WriteLine (member1.Equals(member1_W));
Console.WriteLine (member1.Equals(member1_C));
Console.WriteLine (member1_W.Name);
Console.WriteLine (member1_C.Name);

Console.WriteLine ("Case 2");
var memberList = members.ToList ();
var member1inList = memberList.FirstOrDefault (m => m.Index == 1);
var member1inList_W = memberList.FirstOrDefault (m => m.Index == 1);
member1inList.Name = "Yang SHEN (Case 2)";
Console.WriteLine (member1inList.Equals(member1inList_W));
Console.WriteLine (member1inList_W.Name);

Console.WriteLine ("Case 3");
var member2 = memberList[memberList.FindIndex(m=>m.Index ==2)];
var member2_W = memberList[memberList.FindIndex(m=>m.Index ==2)];
member2.Name = "Yang SHEN (Case 3)";
Console.WriteLine (member2.Equals(member2_W));
Console.WriteLine (member2_W.Name);

'''

不看运行结果，目测一下各个Console.WriteLine的输出是什么？？

..............................................................................................

有意思，同样通过 FirstOrDefault 获得一个集合中的对象，不过，IEnumerable每次都会返回不同的实例，而List 则返回的是同一个实例:)