`Array.Reverse`

This inverts the order of elements. It can act upon an entire array, or just part of an array (a range). It can be used to sort in reverse—simply call Reverse after Sort.

An internal method

Array.Reverse uses an internal, optimized method. It would be hard to develop a faster one in VB.NET code. Usually this built-in is preferred.

An example

Let's begin with this program. The initial array is pointed to by the reference variable a. Then, we reverse that array with Array.Reverse(a). The return value is not used.

Finally We reverse only the first two elements by using the parameters 0 (the first index) and 2 (the count of elements to reverse).

Tip Reverse is found on the Array type. It is a static (shared) function. We call it with a composite name.

Module Module1
    Sub Main()
        Dim a() As Integer = {1, 4, 6, 10}

        For Each v As Integer In a
            Console.WriteLine(v)
        Next
        Console.WriteLine()

        ' Reverse entire array.
        Array.Reverse(a)

        For Each v As Integer In a
            Console.WriteLine(v)
        Next
        Console.WriteLine()

        ' Reverse part of array.
        Array.Reverse(a, 0, 2)

        For Each v As Integer In a
            Console.WriteLine(v)
        Next
    End Sub
End Module1
4
6
10

10
6
4
1

6
10
4
1

A discussion

The implementation of .NET methods is relevant because it tells us whether they will be efficient. Array.Reverse calls an internal method called TrySZReverse.

Tip This is in unmanaged code. It is likely faster in most situations because of unmanaged optimizations.

`Reverse` `string`

With Array.Reverse we can reverse the ordering of chars in a string. We first use ToCharArray to convert a string to a char array.

A summary

We reverse an entire array or only parts (ranges) of an array with Array.Reverse. The type of the elements in the array are not important—they are not sorted or changed.