Can you inherit a sub new (Constructor) with parameters in VB?
In the code below I receive the compile error
Error Too many arguments to 'Public Sub New()'
on the Dim TestChild As ChildClass = New ChildClass("c"). I do not receive it on TestChild.Method1() even though they are both on the base class I am inheriting from.
Public Class BaseClass Public ReadOnly Text As String Public Sub New(ByVal SetText As String) Text = SetText End Sub Public Sub New() Text = "" End Sub End Class Public Class ChildClass Inherits BaseClass End Class Public Class TestClass Sub Test() Dim TestChild As ChildClass = New ChildClass("c") TestChild.Method1() End Sub End Class
I could change the child class to:
Public Class ChildClass Inherits BaseClass Public Sub New (ByVal SetText As String) MyBase.New(SetText) End Class End Class
As suggested below but I do not have to do that for Method 1 or other inherited methods and I am looking for the cleanest code possible. This may be a limitation in the system with inheriting parameterized New statements but I can not find it documented anywhere. If it is required then I would like to see the documentation.
The behavior that you are seeing is "By Design". Child classes do not inherti constructors from their base types. A child class is responsible for defining it's own constructors. Additionally it must ensure that each constructor it defines either implicitly or explicitly calls into a base class constructor or chains to another constructor in the same type.
You will need to define the same constructor on all of the child classes and explicitly chain back into the base constructor via MyBase.New. Example
Class ChildClass Inherits BaseClass Public Sub New(text As String) MyBase.New(text) End Sub End Class
The documentation you are looking for is section 9.3.1 of the VB Language specification.
I think the most relevant section is the following (roughly start of the second page)
If a type contains no instance constructor declarations, a default constructor is automatically provided. The default constructor simply invokes the parameterless constructor of the direct base type.
This does not explicitly state that a child class will not inherit constructors but it's a side effect of the statement.
Parameterized Constructors cannot be inherited in the same way as instance methods. You need to implement the constructor in the child class and then call the parent's constructor using MyBase.
Public Class ChildClass Inherits BaseClass Public Sub New (ByVal SetText As String) MyBase.New(SetText) End Class End Class Public Class TestClass Public TestChild AS New ChildClass("c") End Class
This limitation is not VB specific. From what I can gather, it's definately not possible in C#, Java or C++ either.
Here is one related post with the same question about C++: c-superclass-constructor-calling-rules