How to replace a object in place?

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Lei Jiang - 28 Nov 2004 11:43 GMT

For example :

class A
{
int a;
}

class B : A
{
int b;
}

There are a lot of instance of A in a system(this means there are a lot of
reference to A), and I want to replace all A with B at runtime and make all
references originally point to A now point to B.

These problem can be stated in another way : how to create object B at the
memory address of A?

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Mattias Sj?gren - 28 Nov 2004 19:10 GMT

>These problem can be stated in another way : how to create object B at the
>memory address of A?

You can't.

Mattias

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Mattias Sjögren [MVP] mattias @ mvps.org
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Heath Stewart [MSFT] - 29 Nov 2004 08:01 GMT

I'm not sure what you're trying to accomplish, but if you require that
you can do this often in your code you might consider a level of
indirection. That is, your objects that currently reference A (and you
want to reference B, which is possible since B derives from A) then they
should reference X, where X references A (or B). Class X would not be in
the inheritence chain derived from A. This would allow you to change
what X references while all the objects referencing X should get their
reference to the A base class from X.

This is similar to System.WeakReference, except that it serves a
different purpose in a similar manner.

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Heath Stewart
Software Design Engineer
Developer Division Sustained Engineering
Microsoft Corporation

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Lei Jiang - 03 Dec 2004 01:53 GMT

Thanks! In fact it's a design problem.

> I'm not sure what you're trying to accomplish, but if you require that
> you can do this often in your code you might consider a level of
[quoted text clipped - 7 lines]
> This is similar to System.WeakReference, except that it serves a
> different purpose in a similar manner.

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How to replace a object in place?

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