Why Overloads needed

[Lee Silver]

In a base class I have the following 2 declarations:

Overridable Sub Remove(ByVal wIndex As Integer)
and

Overridable Sub Remove(ByVal wValue As Object)

In an immediately derived class I have the following declaration:

Overloads Overrides Sub Remove(ByVal wIndex As Integer)

Why is Overloads needed in the derived class? Without it intellisense tells me
"Remove shadows an overloadable method in the base class. If you want to
overload the base method this method must be declared Overloads?" Since the
signatures of the 2 methods are the same, I would think the compiler could
determine that the derived method is overriding the Remove(Integer) vs
Remove(Object). What am I missing?

Is it accurate to deduce, based on the intellisense message, that if Remove
weren't overloaded in the base cass I wouldn't need Overloads in the derived one?

--
// Lee Silver
// Information Concepts Inc.
// http://www.information-concepts.com

Facilitating the automated conversion of Data into Information
since 1982

[Lee Silver]

Jay:

Your derived class currently does not have an overloaded Item property, if
you add an overloaded Item property to the base. Your derived class still
will not have an overloaded Item property!

I don't mind adding the Overloads keyword; and I don't want to beat this to
death or be dense -- but I do want to understand...

My base and derived classes each have a single Item property; so it's not
overloaded in either. You state that if I add an overloaded Item to my base I
still won't have one in my derived class. I agree; but I don't see how that's
different than the way my Remove methods are currently declared -- the base
class has an overloaded method and the derived class overrides only one of them.

Well, I just tried overloading the Item property in my base class and the Item
declaration in my derived class got flagged as needing Overloads. I then tried
overriding both properties in the derived class and both declaration got
flagged. So it seems that when a method/property is (implicitly) overloaded in
the base class it must be explicitly overloaded in the derived class. I guess I
don't see why the Overrides keyword isn't sufficient.

--
// Lee Silver
// Information Concepts Inc.
// http://www.information-concepts.com

Facilitating the automated conversion of Data into Information
since 1982

[Jay B. Harlow [MVP - Outlook]]

Lee,

My base and derived classes each have a single Item property; so it's not
overloaded in either. You state that if I add an overloaded Item to my base I still won't have one in my derived class. I agree; but I don't see how that's different than the way my Remove methods are currently declared -- Its a versioning thing. ;-) Mostly when you are deriving from class library
classes.

Java for example does it the other way. In Java when you add an overload in
the base any derived classes automatically gain the overload, this has known
to cause problems occasional. The .NET designers decided rather then allow
these potential problems to Shadow by default rather then overload by
default. Of course this may cause other problems, its a tradeoff either
way...

Also you are assuming that the derived class is going to be compiled, what
happens when derived class is already compiled? I can compile an assembly
under version 1.0 of a class library, and run it under version 2.0 of a
class library without recompiling my original assembly...

NOTE: Think of your MainForm class overriding a method in Microsoft's Form
class. When you upgrade to .NET 2.0 if Microsoft added an overload to that
method in the Form class, this may cause problems in your derived class. To
minimize these problems, the default is to Shadow, hence the warning.
different than the way my Remove methods are currently declared -- the base class has an overloaded method and the derived class overrides only one of them.
That's the point! your derived class overrides only one of them. You only
get one of them in the derived class unless you add Overloads!

Again refer to my overload example, when you use intellisense on the
underlord variable, how many Remove methods are listed? How many are listed
for the overlord variable?

Hope this helps
Jay

"Lee Silver" <LS*****@inform ation-concepts.com> wrote in message
news:aa******** *************** ***@msgid.megan ewsservers.com. .. Jay:

Your derived class currently does not have an overloaded Item property, if you add an overloaded Item property to the base. Your derived class still will not have an overloaded Item property!

I don't mind adding the Overloads keyword; and I don't want to beat this

to death or be dense -- but I do want to understand...

My base and derived classes each have a single Item property; so it's not
overloaded in either. You state that if I add an overloaded Item to my base I still won't have one in my derived class. I agree; but I don't see how that's different than the way my Remove methods are currently declared -- the base class has an overloaded method and the derived class overrides only one of them.
Well, I just tried overloading the Item property in my base class and the Item declaration in my derived class got flagged as needing Overloads. I then tried overriding both properties in the derived class and both declaration got
flagged. So it seems that when a method/property is (implicitly) overloaded in the base class it must be explicitly overloaded in the derived class. I guess I don't see why the Overrides keyword isn't sufficient.

--
// Lee Silver
// Information Concepts Inc.
// http://www.information-concepts.com

Facilitating the automated conversion of Data into Information
since 1982

[Lee Silver]

Jay:

I think I got it now. Thanks for your patience in explaining it.
--
// Lee Silver
// Information Concepts Inc.
// http://www.information-concepts.com

Facilitating the automated conversion of Data into Information
since 1982

Java for example does it the other way. In Java when you add an overload in
the base any derived classes automatically gain the overload, this has known
to cause problems occasional. The .NET designers decided rather then allow
these potential problems to Shadow by default rather then overload by
default. Of course this may cause other problems, its a tradeoff either
way...

Also you are assuming that the derived class is going to be compiled, what
happens when derived class is already compiled? I can compile an assembly
under version 1.0 of a class library, and run it under version 2.0 of a
class library without recompiling my original assembly...

NOTE: Think of your MainForm class overriding a method in Microsoft's Form
class. When you upgrade to .NET 2.0 if Microsoft added an overload to that
method in the Form class, this may cause problems in your derived class. To
minimize these problems, the default is to Shadow, hence the warning.