c# - linq相关问题

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Comparer.csd
{
    class Program
    {
        /* Confusion is regarding how ToList() method works. Does it do the deep copy or shallow copy??

        /**********OUTPUT
         a a b
         a b c
         a c a
        -----------------
         a a b
         a c a
        -----------------
        1
        2
        3
        OUTPUT ENDS************/

        static void Main(string[] args)
        {
            List<test> list = new List<test>();
            list.Add(new test("a", "b", "c"));
            list.Add(new test("a", "c", "a"));
            list.Add(new test("a", "a", "b"));

            /// sort the list based on first name and last name

            IEnumerable<test> soretedCollection = from t in list
                                     orderby t._fname ascending, t._mname ascending
                                     select t;
            Print(soretedCollection);
            /// remove the first object from the list
            list.RemoveAt(0);
            /// print the list .
            /// Removal of the item from the list is reflected here so I guess sorted collection and list both 
            /// are refering the same data structure
            /// what if I will do 
            /// list = soretedCollection.ToList<test>(); /// is it going to change the reference of the list if some other object 
            /// is holding the reference??
            Print(soretedCollection);

            Dictionary<int, int> dic = new Dictionary<int, int>();            
            dic.Add(1, 1);
            dic.Add(2, 1);
            dic.Add(3, 1);
            List<int> keys = dic.Keys.ToList<int>();
            /// remove the dictionary entry with key=2
            dic.Remove(2);
            /// how come this time it did not remove the second item becuase it is removed from the dictionary.
            for (int i = 0; i < keys.Count; ++i)
            {
                Console.WriteLine(keys[i].ToString());
            }

            Console.Read();
        }

        static void Print(IEnumerable<test> list)
        {
            foreach (test t in list)
            {
                t.Print();
            }
            Console.WriteLine("---------------------");
        }
    }

}

Answer 1

调用.ToList()强制执行完整的枚举 - 其结果是与原始枚举不同的列表，因此之后的任何更改.ToList()都不会反映在该列表中。此列表中的实际项目与@Johannes Rudolph 指出的原始枚举中的相同（相同的对象引用） - 所以是的，这是一个浅拷贝。

The IEnumerable<test> though will be lazily executed over the source collection - only when you actively enumerate the items (i.e. by using foreach or .ToList()) will the enumeration create an Enumerator that takes the source collection as it is at that point in time - that means if there are changes in the underlying collection before the Enumerator is created these will be reflected in the enumeration.

Answer 2

ToList将始终创建列表的浅表副本，即返回的列表将引用与源相同的对象IEnumerable，但返回的列表是源的副本。

请参阅MSDN。