application of sealed keyword

[Zeng]

Would somebody know when we should seal a class? Shouldn't all classes be
open up for inheritance?

Thanks!

[Frank Oquendo]

Zeng wrote:

Would somebody know when we should seal a class? Shouldn't all
classes be open up for inheritance?

That's the whole point: that decision is left to the designer.

--
There are 10 kinds of people. Those who understand binary and those who
don't.

http://code.acadx.com
(Pull the pin to reply)

[William Ryan]

There are some things that you don't want inheritable. The main thing that
comes to mind is that i fyou don't have to worry about anyone inheriting
from your class, you can change virtual function invokes to non-virtual
invokes. May not sound like a big deal, but it can be. Granted, there
aren't a whole lot of instances for this, but there are enough for it to be
noteworthy. Another instance is when you may have all static members

http://msdn.microsoft.com/library/de...tml/copybr.asp
"Zeng" <zz*@nonospam.c om> wrote in message
news:OO******** ******@TK2MSFTN GP12.phx.gbl...

Would somebody know when we should seal a class? Shouldn't all classes be
open up for inheritance?

Thanks!

[Zeng]

Thanks for replying, I can see the first instance you pointed out, but the
second one..hm, if the guy next door wants to inherit my class which has all
staic members, then it would be up to him, there isn't a design issue there.

"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:Oq******** ******@TK2MSFTN GP09.phx.gbl...

There are some things that you don't want inheritable. The main thing that comes to mind is that i fyou don't have to worry about anyone inheriting
from your class, you can change virtual function invokes to non-virtual
invokes. May not sound like a big deal, but it can be. Granted, there
aren't a whole lot of instances for this, but there are enough for it to be noteworthy. Another instance is when you may have all static members

http://msdn.microsoft.com/library/de...tml/copybr.asp "Zeng" <zz*@nonospam.c om> wrote in message
news:OO******** ******@TK2MSFTN GP12.phx.gbl...

Would somebody know when we should seal a class? Shouldn't all classes be open up for inheritance?

Thanks!

[William Ryan]

If the class by design had static members, mixing them could cause problems.
Think about Brushes for instance....
"Zeng" <zz*@nonospam.c om> wrote in message
news:%2******** ********@TK2MSF TNGP10.phx.gbl. ..

Thanks for replying, I can see the first instance you pointed out, but the
second one..hm, if the guy next door wants to inherit my class which has all staic members, then it would be up to him, there isn't a design issue there.
"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:Oq******** ******@TK2MSFTN GP09.phx.gbl...

There are some things that you don't want inheritable. The main thing

that

comes to mind is that i fyou don't have to worry about anyone inheriting
from your class, you can change virtual function invokes to non-virtual
invokes. May not sound like a big deal, but it can be. Granted, there
aren't a whole lot of instances for this, but there are enough for it to

be

noteworthy. Another instance is when you may have all static members

http://msdn.microsoft.com/library/de...tml/copybr.asp

"Zeng" <zz*@nonospam.c om> wrote in message
news:OO******** ******@TK2MSFTN GP12.phx.gbl...

Would somebody know when we should seal a class? Shouldn't all classes be open up for inheritance?

Thanks!

[Zeng]

Would you please be more specific? I'm not quite following your example.
Thanks!
"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:%2******** ********@tk2msf tngp13.phx.gbl. ..

If the class by design had static members, mixing them could cause problems. Think about Brushes for instance....
"Zeng" <zz*@nonospam.c om> wrote in message
news:%2******** ********@TK2MSF TNGP10.phx.gbl. ..

Thanks for replying, I can see the first instance you pointed out, but the second one..hm, if the guy next door wants to inherit my class which has

all

staic members, then it would be up to him, there isn't a design issue

there.

"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:Oq******** ******@TK2MSFTN GP09.phx.gbl...

There are some things that you don't want inheritable. The main thing

that

comes to mind is that i fyou don't have to worry about anyone inheriting from your class, you can change virtual function invokes to non-virtual invokes. May not sound like a big deal, but it can be. Granted, there aren't a whole lot of instances for this, but there are enough for it to

be

noteworthy. Another instance is when you may have all static members

http://msdn.microsoft.com/library/de...tml/copybr.asp "Zeng" <zz*@nonospam.c om> wrote in message
news:OO******** ******@TK2MSFTN GP12.phx.gbl...
>
> Would somebody know when we should seal a class? Shouldn't all

classes be

> open up for inheritance?
>
> Thanks!
>
>

[Zeng]

By the way, about the first design usage, you could just use the scope of
your class if you want to avoid calling virtual function; in addition, with
a good design, the override method of a derived class should always replace
the functionality of the one it overrides

"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:%2******** ********@tk2msf tngp13.phx.gbl. ..

If the class by design had static members, mixing them could cause problems. Think about Brushes for instance....
"Zeng" <zz*@nonospam.c om> wrote in message
news:%2******** ********@TK2MSF TNGP10.phx.gbl. ..

Thanks for replying, I can see the first instance you pointed out, but the second one..hm, if the guy next door wants to inherit my class which has

all

staic members, then it would be up to him, there isn't a design issue

there.

"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:Oq******** ******@TK2MSFTN GP09.phx.gbl...

There are some things that you don't want inheritable. The main thing

that

comes to mind is that i fyou don't have to worry about anyone inheriting from your class, you can change virtual function invokes to non-virtual invokes. May not sound like a big deal, but it can be. Granted, there aren't a whole lot of instances for this, but there are enough for it to

be

noteworthy. Another instance is when you may have all static members

http://msdn.microsoft.com/library/de...tml/copybr.asp "Zeng" <zz*@nonospam.c om> wrote in message
news:OO******** ******@TK2MSFTN GP12.phx.gbl...
>
> Would somebody know when we should seal a class? Shouldn't all

classes be

> open up for inheritance?
>
> Thanks!
>
>

[William Ryan]

Zeng:

You're right, you could. However, that's a lot of work when you could just
seal it. There's almost always a few ways to get somewhere, but some
routes are more direct.
"Zeng" <zz*@nonospam.c om> wrote in message
news:%2******** **********@tk2m sftngp13.phx.gb l...

By the way, about the first design usage, you could just use the scope of
your class if you want to avoid calling virtual function; in addition, with a good design, the override method of a derived class should always replace the functionality of the one it overrides

"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:%2******** ********@tk2msf tngp13.phx.gbl. ..

If the class by design had static members, mixing them could cause problems.

Think about Brushes for instance....
"Zeng" <zz*@nonospam.c om> wrote in message
news:%2******** ********@TK2MSF TNGP10.phx.gbl. ..

Thanks for replying, I can see the first instance you pointed out, but the second one..hm, if the guy next door wants to inherit my class which has

all

staic members, then it would be up to him, there isn't a design issue

there.

"William Ryan" <do********@nos pam.comcast.net > wrote in message
news:Oq******** ******@TK2MSFTN GP09.phx.gbl...
> There are some things that you don't want inheritable. The main

thing that
> comes to mind is that i fyou don't have to worry about anyone

inheriting > from your class, you can change virtual function invokes to non-virtual > invokes. May not sound like a big deal, but it can be. Granted, there > aren't a whole lot of instances for this, but there are enough for it to

be
> noteworthy. Another instance is when you may have all static

members >
>

http://msdn.microsoft.com/library/de...tml/copybr.asp

> "Zeng" <zz*@nonospam.c om> wrote in message
> news:OO******** ******@TK2MSFTN GP12.phx.gbl...
> >
> > Would somebody know when we should seal a class? Shouldn't all classes be
> > open up for inheritance?
> >
> > Thanks!
> >
> >
>
>

[Sherif ElMetainy]

Hello

First: If the sealed class is inheriting another class, using the sealed
keyword either in the method or class declaration make the CLR convert all
calls from virtual to normal method calls, because the runtime knows that
this method and can't be overriden. This can improve performance.

Second. When the class designer knows that the overriding of his method can
affect the functionality of his class. For example a method that performs a
security check before making a call to another method. The inheritor of the
method can override the method and calling the other method directly without
the security check, so you may want to prevent anyone from doing that.

Third, if the class has only static fields and properties, it doesn't make
sense to inherit the class. So the class designer can choose to seal his
class to avoid confusion.

Best regards

Sherif

"Zeng" <zz*@nonospam.c om> wrote in message
news:OO******** ******@TK2MSFTN GP12.phx.gbl...

Would somebody know when we should seal a class? Shouldn't all classes be
open up for inheritance?

Thanks!

[Zeng]

Thanks for responding, among the three, I could see the first one being a
good reason for sealed keyword.

For the second one, if security is checked inside a loose method like that,
I can just wrap the class (~ private inheritance in C++ ) and call directly
whatever method I want w/o going through the security checking method. It
sounds to me that a bigger design issue exists for the example you described

For the third, if someone wants to inherit my static-method-only class then
be it, no programmer should or would inherit a class that has nothing to be
inherited, and because there isn't a un-planned consequence, we shouldn't
have to force a policy on it.

Thanks!

"Sherif ElMetainy" <el************ *@wayout.net.NO SPAM> wrote in message
news:OI******** ******@tk2msftn gp13.phx.gbl...

Hello

First: If the sealed class is inheriting another class, using the sealed
keyword either in the method or class declaration make the CLR convert all
calls from virtual to normal method calls, because the runtime knows that
this method and can't be overriden. This can improve performance.

Second. When the class designer knows that the overriding of his method can affect the functionality of his class. For example a method that performs a security check before making a call to another method. The inheritor of the method can override the method and calling the other method directly without the security check, so you may want to prevent anyone from doing that.

Third, if the class has only static fields and properties, it doesn't make
sense to inherit the class. So the class designer can choose to seal his
class to avoid confusion.

Best regards

Sherif

"Zeng" <zz*@nonospam.c om> wrote in message
news:OO******** ******@TK2MSFTN GP12.phx.gbl...

Would somebody know when we should seal a class? Shouldn't all classes be open up for inheritance?

Thanks!