Shortcut for vb null and Any() checks

Question

I'm sorry if asked before...if so, I did not find it.

I was reading A Shortcut for c# null and Any() checks and I saw the accepted answer. I understand the answer, although most people use x.Items?.Any() ?? false.

My question is: How to do this is VB.NET

Could I just simply write

If x.Items?.Any() Then

or do I need

If x.Items?.Any() = True Then

While if (x.Items?.Any()) does not compile in C#, they both do in VB...but that doesn't always mean they are both correct :-)

If Items is nullable, so Any() will return bool?. So it should be = True to avoid null. — Berkay Yaylacı, Mar 03 '21 at 13:30
As far as I get it, this compiles because VB autocasts bool? to bool. If the values is really null at runtime, this will crash obviously. But will this ever be null? — diedie2, Mar 03 '21 at 13:34
Actually, both of them won't crash in the if case. Because there is exact type comparision. If items is null, either true or false will not equal to null. — Berkay Yaylacı, Mar 03 '21 at 13:40
I can't even test on .NET Fiddle :s https://dotnetfiddle.net/5K5GE5 — diedie2, Mar 03 '21 at 14:08
The VB equivalent to C# `??` is the two-argument operator form of `If`. That is, `x ?? y` in C# is the same as `If(x, y)` in VB. — Craig, Mar 03 '21 at 16:01

Zev Spitz · Answer 1 · 2021-03-03T14:38:59.617

1

When I tested the following on LinqPad:

Dim lst As List(Of Vehicle) = Nothing
If lst?.Any Then
    Console.WriteLine("True")
Else
    Console.WriteLine("False")
End If

it works just fine, and prints False, even with Option Strict On.

It also works from within Visual Studio in a .NET 5 console app.

It would seem that Visual Basic supports using Boolean? in the test of an If statement.

And it now seems to work on .NET Fiddle.

edited Mar 03 '21 at 14:38

answered Mar 03 '21 at 14:28

Zev Spitz

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Your code will resolve to `False` because the `?` shortcut resolves to null/Nothing and the `Any()` is not even tested. If `lst` was not null but empty (ie `= New List(Of Vehicle)`), it would resolve to `False` due to the `Any()` test. – SteveCinq Mar 03 '21 at 16:26
@SteveCinq I'm not quite sure what you're trying to say. Isn't that the point? Whether the list is `Nothing`, or the list is empty, the "else" branch of the `If` will be executed. – Zev Spitz Mar 03 '21 at 16:30
Just highlighting the "why" side. Not a criticism. – SteveCinq Mar 03 '21 at 17:11

score 0 · Accepted Answer · answered Mar 03 '21 at 14:29

After doing some tests on .NET Fiddle I found out both work

Imports System
Imports System.Linq
            
Public Module Module1
  public Class Vehicle

  End Class

  Public Sub Main()

    Dim x as System.Collections.Generic.List(Of Vehicle)
    
    Dim y as System.Collections.Generic.List(Of Vehicle)
    y = new System.Collections.Generic.List(of Vehicle)
    
    Dim z as System.Collections.Generic.List(Of Vehicle)
    z = new System.Collections.Generic.List(of Vehicle)
    
    z.Add(new Vehicle())
        
    If (x?.Any() = True) Then
        Console.WriteLine("X YES")
    Else
        Console.WriteLine("X NO")
    End If
    
    If (x?.Any()) Then
        Console.WriteLine("X YES")
    Else
        Console.WriteLine("X NO")
    End If
    
    If (y?.Any() = True) Then
        Console.WriteLine("Y YES")
    Else
        Console.WriteLine("Y NO")
    End If
    
    If (y?.Any()) Then
        Console.WriteLine("Y YES")
    Else
        Console.WriteLine("Y NO")
    End If
    
    If (z?.Any() = True) Then
        Console.WriteLine("Z YES")
    Else
        Console.WriteLine("Z NO")
    End If
    
    If (z?.Any()) Then
        Console.WriteLine("Z YES")
    Else
        Console.WriteLine("Z NO")
    End If
End Sub
End Module

will result in

X NO
X NO
Y NO
Y NO
Z YES
Z YES

as excpected

What happens if you remove the parentheses? – Zev Spitz Mar 03 '21 at 14:31 — Zev Spitz, Mar 03 '21 at 14:31

Shortcut for vb null and Any() checks

2 Answers2