Redim Preserve in C#?

I was shocked to find out today that C# does not support dynamic sized arrays. How then does a VB.NET developer used to using ReDim Preserve deal with this in C#?

At the beginning of the function I am not sure of the upper bound of the array. This depends on the rows returned from the database.

Solution 1:

VB.NET doesn't have the idea of dynamically sized arrays, either - the CLR doesn't support it.

The equivalent of "Redim Preserve" is Array.Resize<T> - but you must be aware that if there are other references to the original array, they won't be changed at all. For example:

using System;

class Foo
{
    static void Main()
    {
        string[] x = new string[10];
        string[] y = x;

        Array.Resize(ref x, 20);
        Console.WriteLine(x.Length); // Prints out 20
        Console.WriteLine(y.Length); // Still prints out 10
    }
}

Proof that this is the equivalent of Redim Preserve:

Imports System

Class Foo
    Shared Sub Main()
        Dim x(9) as String
        Dim y as String() = x

        Redim Preserve x(19)
        Console.WriteLine(x.Length)
        Console.WriteLine(y.Length)
    End Sub
End Class

The two programs are equivalent.

If you truly want a dynamically sized collection, you should use List<T> (or something similar). There are various issues with using arrays directly - see Eric Lippert's blog post for details. That's not to say you should always avoid them, by any means - but you need to know what you're dealing with.

Solution 2:

Use ArrayLists or Generics instead

Solution 3:

Use a List<T>. It will dynamically size as needed.

Solution 4:

You really shouldn't be using ReDim, it can be every expensive. I prefer List(Of T), but there are many options in this area.

That said, you had a question and here is your answer.

x = (int[]) Utils.CopyArray((Array) x, new int[10]);