CODEWITHSUNDEEP
vb.netfunctionparameterscompiler-errors
BenM
BenM

Reputation: 4278

Being able to pass in an argument to a function with no parameters

I'm using VB.NET currently and I've come across an issue. This is my class:

Public class foo

    Private _bar As Integer
    Private _name As String

    Public Sub New(bar As Integer)
        Me._bar = bar
        Me._name = getName(bar) '//Passing in an argument where it is not needed
    End Sub

    Private Function getName() As String

        '//Get name from database using _bar as a lookup(it's essentially a primary key)
        '//Name is obtained successfully (checked when debugging)
        '//Return name

    End Function

End Class

I am able to run this code despite passing in an argument to getName where it has no parameters. However, when I run it, the Me._name field always ends up with an empty string (not a null value as it initially starts out as) but I know that the getNamemethod is returning the correct string as I checked it during debugging. If I remove the unneeded parameter then it works as expected and Me._name gets the returned value.

Why am I able to pass an argument where there shouldn't be one and not get any errors showing up in my error list? I tried this on a coworkers computer and they got a "Too many arguments" error.

Upvotes: 4

Views: 1985

Answers (2)

Bjørn-Roger Kringsjå
Bjørn-Roger Kringsjå

Reputation: 9981

Chars is default property of the String class. 

Public NotInheritable Class [String]

    <__DynamicallyInvokable> _
    Public ReadOnly Default Property Chars(ByVal index As Integer) As Char
        <MethodImpl(MethodImplOptions.InternalCall), SecuritySafeCritical, __DynamicallyInvokable> _
        Get
    End Property

End Class

That is why you can call:

getName(bar)

Which is the equivalent to 

getName.Chars(bar)

Now, if the String class didn't have any default property you would get an error saying Expression is not an array or a method, and cannot have an argument list.. 

Public Class foo

    Private _bar As Integer
    Private _name As [String]

    Public Sub New(bar As Integer)
        Me._bar = bar
        Me._name = getName(bar) '//Passing in an argument where it is not needed
    End Sub

    Private Function getName() As [String]
        '//Get name from database using _bar as a lookup(it's essentially a primary key)
        '//Name is obtained successfully (checked when debugging)
        '//Return name
    End Function

End Class

Public NotInheritable Class [String]

    Public ReadOnly Property Chars(index As Integer) As Char
        Get

        End Get
    End Property

End Class

Upvotes: 2

ekad
ekad

Reputation: 14614

We can call a function/sub with or without parentheses in VB.NET, so this

getName(bar)

is actually the same as this

getName()(bar)

and that's why there's no errors.

Furthermore, getName(bar) won't pass bar as a parameter to getName function, but it will return the (bar+1)th character of the value returned by getName().

For example if we change getName function to this

Private Function getName() As String
    Return "test"
End Function

then getName(1) will be the same as getName()(1) and it will return the second character of "test", which is "e".

Upvotes: 7

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