Type inference

In Visual Basic 6.0 it is very common to use variables without declaring them. When the Upgrade Wizard finds variables without a declaration, it writes Error Warning and Issue (EWI) 1037 (UPGRADE_WARNING: Couldn't resolve default property of object ‘x’) for every use of the variable as shown in the example below. The variable declaration upgrade warning can occur frequently in some VB projects. It typically represents 30% to 40% of total EWIs. The Visual Basic Upgrade Companion can eliminate most of the occurrences of this upgrade warning. This reduction represents about 10% to 20% of the total EWIS, depending on the design of the project.

In this example the Upgrade Wizard declares all variables as Object while the Visual Basic Upgrade Companion declares them as Byte.

        PrivateSub Command1_Click()
        a=5
        b = 10
        c = 5 + 10
        EndSub
    

Private Sub Command1_Click(ByVal eventSender As System.Object, …
    Dim c As Object
    Dim b As Object
    Dim a As Object
    'UPGRADE_WARNING: Couldn't resolve default property of object a.
    a=5
    'UPGRADE_WARNING: Couldn't resolve default property of object b.
    b = 10
    'UPGRADE_WARNING: Couldn't resolve default property of object c.
    c = 5 + 10
End Sub

Private Sub Command1_Click(...) Handles Command1.Click
    Dim a As Byte =5
    Dim b As Byte = 10
    Dim c As Byte = 5 + 10
End Sub

private void Command1_Click(…)
    byte a = 5;
    byte b = 10;
    byte c = 5 + 10;

The function "fibonnacci" in VB6 is declared without return type. Also variable "j" does not have a specific type. Since both the function and the parameter don’t have a type, the Upgrade Wizard declares them as an Object.

The Visual Basic Upgrade Companion analyzes the function and determines that the return type is Integer and the type of parameter "j" is Byte.

Public Function fibonnacci(j)
    If j = 0 Or j = 1 Then
        fibonnacci = 1
    Else
        fibonnacci = fibonnacci(j -1) + fibonnacci(j -2)
    End If
End Function

Public Function fibonnacci(ByRef j As Object) As Object
    'UPGRADE_WARNING: Couldn't resolve default property of object j.
    If j = 0 Or j = 1 Then
        'UPGRADE_WARNING: 'Couldn't resolve default property of object fibonnacci.'
        fibonnacci = 1
    Else
        'UPGRADE_WARNING: 'Couldn't resolve default property of property of object j.
        'UPGRADE_WARNING: 'Couldn't resolve default property of object fibonnacci(j -2).
        'UPGRADE_WARNING: 'Couldn't resolve default property of object fibonnacci().
        'UPGRADE_WARNING: 'Couldn't resolve default property of object fibonnacci.
        fibonnacci = fibonnacci(j -1) + fibonnacci(j -2)
    End If
End Function

Public Function fibonnacci(ByVal j As Byte) As Integer
    If j = 0 Or j = 1 Then
        Return 1
    Else
        Return fibonnacci(j -1) + fibonnacci(j -2)
    End If
End Function

public int fibonnacci(byte j)
    if (j == 0 || j == 1)
        return 1;
    else
        return fibonnacci(j -1) + fibonnacci(j -2);
}