What is the difference between the Me and the MyClass keywords? I
understand Me that it represents the specific instance of the class.
When you're inside the object instance, it refers to itself using the
Me keyword. What is the MyClass keyword used for?
24  3567 
MyClass is used in situations where the current class (me) overrides a
member from the base class (MyBase). Now, let's assume the in the base
class version of the overridden member, you want to ensure that a BASE class
member gets used by the child class, you would use the MyClass keyword in
the BASE class's overrideable member.
In the end, when the child class calls its own version of an overridable
member, the value from the BASE class that was marked as MyClass still gets
used.
"Water Cooler v2" <wt*****@yahoo. com> wrote in message
news:11******** *************@o 13g2000cwo.goog legroups.com... What is the difference between the Me and the MyClass keywords? I
understand Me that it represents the specific instance of the class.
When you're inside the object instance, it refers to itself using the
Me keyword. What is the MyClass keyword used for?
On 2005-09-03, Water Cooler v2 <wt*****@yahoo. com> wrote: What is the difference between the Me and the MyClass keywords? I
understand Me that it represents the specific instance of the class.
When you're inside the object instance, it refers to itself using the
Me keyword. What is the MyClass keyword used for?
MyClass ignores any derived class overrides. This is one of those
instances where the help file is actually very helpful. Either type MyClass into
help, or check out... http://msdn.microsoft.com/library/de...keymyclass.asp
(sorry about any breaks in the url)
On 2005-09-03, Scott M. <s-***@nospam.nosp am> wrote: MyClass is used in situations where the current class (me) overrides a
member from the base class (MyBase). Now, let's assume the in the base
class version of the overridden member, you want to ensure that a BASE class
member gets used by the child class, you would use the MyClass keyword in
the BASE class's overrideable member.
In the end, when the child class calls its own version of an overridable
member, the value from the BASE class that was marked as MyClass still gets
used.
I thought I understood this stuff, but I don't follow that at all. How
do you "mark a value as MyClass"? I thought MyClass was something you
used when invoking a member, not when declaring it.
And AFAIK, a child class is always going to get it's own overridden
members unless it specifically calls into the base class. The base class
can ignore the overrides in its own function calls, but can't make any
changes to the function calls that the child class makes.
Am I missing something, or just confused by the wording here?
dfoster,
I think your understanding is right. Scott M. probably did not word it
correctly.
And now, that link you have mentioned from the MSDN brings us to a very
important question.
What if I changed the interface/pointer type of the object from whom I
invoke the MyMethod sub to that of the base class.
So, instead of:
Dim TestObj As DerivedClass = New DerivedClass
TestObj.UseMe() ' Displays "Derived class string".
TestObj.UseMyCl ass() ' Displays "Base class string".
TestObj.MyMetho d()
that the documentation has, what if I do this:
Dim Base As BaseClass = New DerivedClass
Base.MyMethod()
Base.UseMe()
Base.UseMyClass ()
It nullifies the v-table entries and shadows the derived class
overrides just as in the previous example. This proves that one must
not expect polymorphic behaviour from your class if you invoke a method
with the MyClass keyword.
Thanks for all your replies.
Regards,
Sathyaish
PS: I am Water Cooler v2. My posting quota on this machine is over, so
I have switched accounts.
On 2005-09-04, Sathyaish <sa*******@gmai l.com> wrote: dfoster,
I think your understanding is right. Scott M. probably did not word it
correctly.
And now, that link you have mentioned from the MSDN brings us to a very
important question.
What if I changed the interface/pointer type of the object from whom I
invoke the MyMethod sub to that of the base class.
It wouldn't matter.
So, instead of:
Dim TestObj As DerivedClass = New DerivedClass
TestObj.UseMe() ' Displays "Derived class string".
TestObj.UseMyCl ass() ' Displays "Base class string".
TestObj.MyMetho d()
That last displays "Derived Class string"
that the documentation has, what if I do this:
Dim Base As BaseClass = New DerivedClass
Base.MyMethod()
Still displays "Derived class string"
Base.UseMe()
Base.UseMyClass ()
It nullifies the v-table entries and shadows the derived class
overrides just as in the previous example. This proves that one must
not expect polymorphic behaviour from your class if you invoke a method
with the MyClass keyword.
I'd word that differently. From the callers POV, you still get
polymorphism. MyMethod will display differently depending on whether the
caller created a BaseClass or a DerivedClass, regardless of whether the
variable is declared as a BaseClass or a DerivedClass. A DerivedClass
instance acts the same way even if you call methods through a variable
declared as BaseClass.
The variable declaration simply doesn't matter, only the definition does,
and that's the essence of polymorphism.
I struggle to think of a use for MyClass that doesn't represent horrible
design. Does anyone know if this is actually used in the framework
anywhere?
>you still get polymorphism.
Surely, you get polymorphism. I meant that *for the method call
qualified by MyClass, the polymorphic behaviour is overlooked/shadowed.*
On 2005-09-04, Sathyaish <sa*******@gmai l.com> wrote: you still get polymorphism.
Surely, you get polymorphism. I meant that *for the method call
qualified by MyClass, the polymorphic behaviour is overlooked/shadowed.*
We might just be saying the same thing, but your example was changing...
Dim TestObj As DerivedClass = New DerivedClass
to
Dim Base As BaseClass = New DerivedClass
That's entirely polymorphic. The caller has no clue that MyClass was
being used anywhere, nor should it. Those two examples result in the
exact same code paths.
I'm not really sure what that example is supposed to show. Changing the
declaration of the instance variable doesn't affect anything.
dfoster,
| I struggle to think of a use for MyClass that doesn't represent horrible
| design. Does anyone know if this is actually used in the framework
| anywhere?
Chaining constructors, such as:
Public Class SomeCollection
Public Const DefaultValue As String = ""
Public Const DefaultCapacity As Integer = 16
Public Sub New()
MyClass.New(Def aultValue, DefaultCapacity )
End Sub
Public Sub New(ByVal capacity As Integer)
MyClass.New(Def aultValue, capacity)
End Sub
Public Sub New(ByVal value As String)
MyClass.New(val ue, DefaultCapacity )
End Sub
Public Sub New(ByVal value As String, ByVal capacity As Integer)
End Sub
...
End Class
Granted you could use Optional parameters instead at the expense of being
friendly to C#...
For methods other then constructors, I cannot think of a good example where
I would, much less have, used it. However I expect if it was not available,
then we would all have good examples of needing it ;-)
Hope this helps
Jay
"dfoster" <df*****@woofix .local.dom> wrote in message
news:sl******** ************@lo calhost.localdo main...
| On 2005-09-04, Sathyaish <sa*******@gmai l.com> wrote:
| > dfoster,
| >
| > I think your understanding is right. Scott M. probably did not word it
| > correctly.
| >
| > And now, that link you have mentioned from the MSDN brings us to a very
| > important question.
| >
| > What if I changed the interface/pointer type of the object from whom I
| > invoke the MyMethod sub to that of the base class.
|
| It wouldn't matter.
|
| >
| > So, instead of:
| >
| > Dim TestObj As DerivedClass = New DerivedClass
| > TestObj.UseMe() ' Displays "Derived class string".
| > TestObj.UseMyCl ass() ' Displays "Base class string".
| > TestObj.MyMetho d()
|
| That last displays "Derived Class string"
|
| >
| > that the documentation has, what if I do this:
| >
| > Dim Base As BaseClass = New DerivedClass
| > Base.MyMethod()
|
| Still displays "Derived class string"
|
| > Base.UseMe()
| > Base.UseMyClass ()
| >
| > It nullifies the v-table entries and shadows the derived class
| > overrides just as in the previous example. This proves that one must
| > not expect polymorphic behaviour from your class if you invoke a method
| > with the MyClass keyword.
|
| I'd word that differently. From the callers POV, you still get
| polymorphism. MyMethod will display differently depending on whether the
| caller created a BaseClass or a DerivedClass, regardless of whether the
| variable is declared as a BaseClass or a DerivedClass. A DerivedClass
| instance acts the same way even if you call methods through a variable
| declared as BaseClass.
|
|
| The variable declaration simply doesn't matter, only the definition does,
| and that's the essence of polymorphism.
|
| I struggle to think of a use for MyClass that doesn't represent horrible
| design. Does anyone know if this is actually used in the framework
| anywhere?
|
|
No, your understanding is wrong and my wording is right.
You don't declare something as MyClass (nor, did I say that you do), you
reference something that way. An example is best...
'************** *************** *************** **
Public Class A
Public Overridable Function DoFoo() As String
'Do something here
End Function
Public Overridable Sub Foo()
MyClass.DoFoo()
End Sub
End Class
'************** *************** *************** **
Public Class B
Inherits A
Public Overrides Function DoFoo() As String
'Do something here
End Function
Public Sub SomethingElse
Foo()
End Sub
End Class
'************** *************** *************** **
If I were to now make an instance of class "B" and call its "SomethingE lse"
method the SomethingElse method from the "B" class then calls the "Foo"
method of the base class.
In the base class (A), the "Foo" method calls an overridable method called
"DoFoo". There is a "DoFoo" method in BOTH classes. Without the "MyClass"
keyword in the base class, the child class would wind up using the
overridden "DoFoo" method in the child class, but because of the "MyClass"
keyword, calling "SomethingE lse" in the child class calls "Foo" in the base
class and "Foo" in the base class uses "DoSomethin g" from the SAME CLASS as
"DoSomethin g" is running (which is the base class).
It is a bit confusing, but if you trace my explanation, you will see that
without the "MyClass" keyword, the base class method "Foo" would use the
child class method "DoFoo" instead of its own.
-Scott
"Sathyaish" <sa*******@gmai l.com> wrote in message
news:11******** **************@ z14g2000cwz.goo glegroups.com.. . dfoster,
I think your understanding is right. Scott M. probably did not word it
correctly.
And now, that link you have mentioned from the MSDN brings us to a very
important question.
What if I changed the interface/pointer type of the object from whom I
invoke the MyMethod sub to that of the base class.
So, instead of:
Dim TestObj As DerivedClass = New DerivedClass
TestObj.UseMe() ' Displays "Derived class string".
TestObj.UseMyCl ass() ' Displays "Base class string".
TestObj.MyMetho d()
that the documentation has, what if I do this:
Dim Base As BaseClass = New DerivedClass
Base.MyMethod()
Base.UseMe()
Base.UseMyClass ()
It nullifies the v-table entries and shadows the derived class
overrides just as in the previous example. This proves that one must
not expect polymorphic behaviour from your class if you invoke a method
with the MyClass keyword.
Thanks for all your replies.
Regards,
Sathyaish
PS: I am Water Cooler v2. My posting quota on this machine is over, so
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