Why does the .NET Array.Resize() method use an ref argument?

Question

Other methods like Array.Sort() don't use ref and yet they change the array.

Also this code confuses me:

using System.Linq;
using System;

namespace jmennyprostor {
    public static void Main(string[] args)
    {
        int[] mojepole = {4,4,5,2,4};
        pole.changearray(mojepole); // this does change mojepole
        pole.resizearray(mojepole); // this magically does not change mojepole
        pole.resizearrayworking(ref mojepole); // this DOES change mojepole
    }

    public class pole 
    {
        public static void changearray(int[] polerole)
        {
            polerole[2] = 44444;
        }

        public static void resizearray(int[] polerole)
        {
            Array.Resize(polerole);
        }

        public static void resizearrayworking(ref int[] polerole)
        {
            Array.Resize(polerole);
        }
    }
}

The following may be helpful: learn.microsoft.com/en-us/dotnet/csharp/programming-guide/… and learn.microsoft.com/en-us/dotnet/csharp/fundamentals/… — It all makes cents
– It all makes cents, Commented Mar 12, 2022 at 3:17
Distinguish modifying the array content from the array object. Array.Resize() creates a new array object, so needs ref. — Hans Passant
– Hans Passant, Commented Mar 12, 2022 at 14:14

David Browne - Microsoft · Accepted Answer · 2022-03-12 12:26:07Z

2

Because the array may not actually be resized. So you pass in a reference to an array of size N, and the method may allocate a new array of size newSize and change your reference to point to the new array.

It has a similar effect as

oldArray = Array.Resize(oldArray, newSize);

if the method returned a reference to the new array instead of using a ref argument.

edited Mar 12, 2022 at 12:26

answered Mar 12, 2022 at 2:53

David Browne - Microsoft

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