C#

George_George wrote:

the code Foo[] FooArray = new Foo[3] creates 3 new instances of Foo

Foo[] FooArray = new Foo[3];
Console.WriteLine(FooArray[0].abc.ToString()); // Null reference exception

George_George wrote:

So this code Foo[] FooArray = new Foo[3] will only create 3 references and make them refer to NULL

George_George wrote:

hen code dic.Values.CopyTo(FooArray, 0) will create 3 instances of Foo class

George_George wrote:

I am confused why do you think the code "dic.Values.CopyTo(FooArray, 0)" is the same as the code "dict.Add(1,new Foo(10))"

George_George wrote:

I think not the reference, but the real new copy is created?

J4amieC wrote:

Im 99% sure you're copying the references not making a new instance.

class Foo
{
    public int abc;

    public Foo (int i)
    {
        abc = i;
    }

}

public static void Main()
{

    Dictionary<int, Foo> dic = new Dictionary<int,Foo>();
    dic.Add(1, new Foo(10));
    dic.Add(2, new Foo(20));
    dic.Add(3, new Foo(30));

    Foo[] FooArray = new Foo[3];

    dic.Values.CopyTo(FooArray, 0);

    // change the 1st one
    FooArray[0].abc = 40;

    // output 40
    Console.WriteLine(dic[1].abc);

    return;
}

George_George wrote:

I think CopyTo will create new instances, other than just make a copy of the reference, right?

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Text;

namespace ConsoleApplication2
{
    class Foo
    {
        public int abc;
        public Foo(int abc)
        {
            this.abc = abc;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {           

            Dictionary<int, foo=""> d = new Dictionary<int, foo="">();
            d.Add(1, new Foo(10));
            d.Add(2, new Foo(20));
            d.Add(3, new Foo(30));

            Foo[] fooArray = new Foo[3];

            d.Values.CopyTo(fooArray, 0);

            Console.WriteLine(d[1].abc);
            Console.WriteLine(fooArray[0].abc);

            Console.WriteLine("Same Instance? {0}", (d[1] == fooArray[0]));
            Console.ReadLine();
        }
    }
}
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