In VB.NET what does it mean to declare a Byte array as New Byte(-1){}

Question

I am trying to understand some VB code that does this:

Public Function Foo( ByVal a as Byte(), ByVal b as Byte(), ByVal Optional c as Byte() = Nothing) as Byte()

  
  <snip>

  c = If(c, New Byte(-1) {} )

  <snip>

End Function

What does it mean to use -1 there? When I use a translator to convert the code to C#, it doesn't like -1 and throws an error that it's out of range and must be non-negative.

Answer 1

In VB.NET, you create an array by specifying the upper bound, e.g.

Dim arr = New Byte(99) {}

creates an array with a Length of 100. If the upper bound is 1 less than the Length and you specify -1 as the upper bound, what's the Length? It's zero, i.e. you created an empty array. Since .NET Framework 4.6, you should be using the Array.Empty method to do that:

c = If(c, Array.Empty(Of Byte)())

c = c ?? Array.Empty<byte>();

I think that C# would also support this:

c ??= Array.Empty<byte>();