"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...
SLE <in**@NOSPAM.da taworx.be> wrote: I know constructors are not inherited from the base class, not in VB.NET
nor C# (nor Java I suppose). I never wondered,but reflecting on the reason
why, I cannot find a solid answer.
Is the reason technical (compiler or CLR limitation) or logical (OOP
best practices)?
It's not always appropriate for a derived class to be able to be
constructed with only the parameters the base class requires. For
instance, System.Object has a parameterless constructor. If
constructors were inherited, *every* class would have to have a
parameterless constructor. What would a parameterless constructor for
FileStream mean?
Well, suppose parameterless constructors actually were inherited, a
parameterless ctor for FileStream could mean nothing :) untill some
Init(params) method was called. Without the latter, other FS methods should
throw exceptions. In other words, *if* ctors were inherited, the FileStream
class would have had a different implementation.
You're right but the case you mention could have been solved at design time.
I simply like to know why the .NET team made the decision not to inherit
constructors (as opposed to e.g. Delphi).
I see some benefits in derived constructors, such as in this simplified
example:
Public Class Person
Private _name As String
Private _age As String
Public Sub New()
End Sub
Public Sub New(ByVal name As String, ByVal age As Integer)
_name = name
_age = age
End Sub
End Class
Public Class Woman
Inherits Person
End Class
1) I cannot instantiate a Woman object with Dim w as New Woman("Justine" ,
2) - the only way is to explicitly add a contructor with the same signature
to the Woman class:
Public Sub New(ByVal name As String, ByVal age As Integer)
MyBase.New(name , age)
End Sub
One should replicate each parametrized ctor of the base class to all derived
classes ... Good thing someone invented copy/paste but this seems more like
writing a book than coding to me ;)
2) Now, suppose a parameter type should change (we do not have something
like generics yet), or a new param should be added (for instance, data of
birth) on the base class, I need the change the constructor of *all* derived
classes.
--
SLE
