arrayVariable() As Object vs. arrayVariable As Object() – not the same in Property declaration?

Question

Until today, I thought that the following two notations are the same (edit: Dim was replaced by Property)

Property arrayVariable() As Object 
Property arrayVariable As Object()

Today I found that former one throws error Option Strict On disallows late binding. while the latter compiles OK in expression dictionary1.TryGetValue(CStr(arrayVariable(0)), result).

Please what is the difference between them?

I would always use the second notation if it also allowed to specify the array dimensions. It doesn't, so I stuck with the first form (less clean one, because part of type specification - parenthesis - are before As) in order to be consistent across declarations. And now I see that even the first one isn't universal...

It really looks like a weak point of Visual Basic that two forms exist for one thing and their usage is not straightforward but has catches like this.

Full source code reproducing the issue:

Public Class Class1
    Dim _A1() As Object
    Dim _A2() As Object

    ReadOnly Property A1() As Object ' 1st form of declaration
        Get
            Return _A1
        End Get
    End Property

    ReadOnly Property A2 As Object() ' 2nd form of declaration
        Get
            Return _A2
        End Get
    End Property
End Class

Sub Main()
    Dim c1 As New Class1
    Dim d1 As New Dictionary(Of String, String)
    Dim value As String = ""
    d1.TryGetValue(CStr(c1.A1(0)), value)  '<- Option Strict On disallows late binding.
    d1.TryGetValue(CStr(c1.A2(0)), value)  '<- No error here.
End Sub

Can you please provide the complete block of code that contains the `dictionary1.TryGetValue(CStr(arrayVariable(0)), result)` code? — Enigmativity, Jan 11 '15 at 03:18
Question already answered here: http://stackoverflow.com/questions/533166/what-is-the-difference-between-dim-v-as-string-and-dim-v-as-string — Joe Uhren, Jan 11 '15 at 03:39
@JoeyJoeJoeJrShabadoo - looks I have discovered the case NOT covered by answers in question you linked :) Try the code yourself... — miroxlav, Jan 11 '15 at 03:41

OneFineDay · Accepted Answer · 2015-01-11T17:40:26.777

The problem is that they are Properties so the () is ignored as an Array specifier and thinks of it as an empty parameter collection. Look at how the compiler see them - even the compiler thinks you had an Object and not a Object() and so in your example the A1(0) is an index of an object which is not defined so it thinks you have done some late binding and made it accept an array.

If you are not using a Property and an Object type either declaration is valid.

Dim data() As String

Same as

Dim data As String()

If you highlight either variable the intellisence shows you:

 Dim data() As String

score 0 · Answer 2 · answered Jan 11 '15 at 04:18

0

Here's the minimum amount of code required to replicate your issue:

Dim y As Object
Dim x = y(0)

This has nothing to do with the declaration of arrays. You're just trying to convert an Object to an array which option strict doesn't allow.

answered Jan 11 '15 at 04:18

Enigmativity

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you made the merit obvious, but the case is not so obvious at property declaration where syntactically a variable definition is seen although function header notation has obviously priority in interpretation of declaration as @OneFineDay noted. – miroxlav Jan 11 '15 at 04:40

score 0 · Answer 3 · edited Jun 20 '20 at 09:12

0

Additional notes:

(not sure why this has been downvoted)

Changing Object to Integer reveals the first form mentioned in question is not taken as declaration.

Public Class Class1
    Dim _A1 As Integer()
    Dim _A2 As Integer()

    ReadOnly Property A1() As Integer
        Get
            Return _A1 
          ' error at above line: Value of type '1-dimensional array of Integer' cannot
          ' be converted to 'Integer'.
        End Get
    End Property
    ReadOnly Property A2 As Integer()
        Get
            Return _A2
        End Get
    End Property
End Class

Proper way is

    ReadOnly Property A1() As Integer()

edited Jun 20 '20 at 09:12

Community

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answered Jan 11 '15 at 04:48

miroxlav

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When the declaration is for a property, fields can be done either way. – OneFineDay Jan 11 '15 at 05:14
@OneFineDay - please could you show what do you mean by "either way"? I'm not sure. – miroxlav Jan 11 '15 at 10:16
@OneFineDay - OK, I understand that for `Dim` both forms of declaration have the same meaning, but this is NOT true for `Property`. I'm not speaking about its backing store, but about property declaration itself, which can be also written without its backing store as `Property A1() As Integer`. Then as you correctly noted, `Property A1() As Integer` and `Property A1 As Integer()` aren't the same. For *Object* type, it won't be reported until such a property is used (tricky!), but for other types, problem is reported immediately. I do not understand downvoting of my answer explaining this. – miroxlav Jan 11 '15 at 19:56
I have no idea who downvoted you. Sure it seems tricky, the difference is with an Object and other DataTypes and how properties are declared - as I stated in my answer. – OneFineDay Jan 11 '15 at 22:23

arrayVariable() As Object vs. arrayVariable As Object() – not the same in Property declaration?

3 Answers3

Additional notes:

Linked