"Jon Skeet [C# MVP]" <sk***@pobox.com> wrote in message
news:MP************************@msnews.microsoft.c om...
SLE <in**@NOSPAM.dataworx.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
