Re: howto decouple in .NET?

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Hi Ben,

Sorry for the misunderstanding.

Perhaps you are looking for the mechanisms in C# for a ¡°compilation
firewall¡±, that is, a mechanism to decouple software components such that
both can compile independently and compilation propagation stops right
there. If that is the case, then the .NET interface type could help for
getting somehow similar effects, depending on the particular situation and
constraints, .NET reflection could be of help also.

In C++, one can inadvertently expose implementation details and increase
coupling: If Foo embeds a private member Bar, then every user of class Foo
also needs to know the layout of class Bar in order to use Foo. In managed
code, the problem doesn¡¯t exist ¨C if a class has a private member, the
rest of the world doesn¡¯t need to know of its existence. You can easily
verify this by declaring a public class Foo, which has a private reference
to an ¡°internal class Bar¡± declared in the same assembly.

However, using types ¡°in name only¡± is not possible in .NET. In C++, it
is possible for a class Foo to use Bar in its interface as an opaque handle
(if the public surface only refers to Bar* or Bar& and an instance of Bar
is NOT embedded in Foo, then the clients of Foo never need the definition
of Bar). Furthermore, if Foo never uses Bar directly in its implementation
(and only passes pointers or references to it to other components instead),
then Foo itself never needs the definition of Bar, either. This is not
achievable in C# - for instance, you cannot declare a public class Foo with
a public method taking or returning a Bar, if Bar is an internal class ¨C
you¡¯ll end up getting compiler errors.

If you are really committed to the lost art of uncoupling code, you might
want to look at ¡°the other way¡± of doing it ¨C declare Bar as internal
and don¡¯t use it in the public interface, but return and take IDs instead,
which you can then map to actual objects (in .NET, they can simply declare
their interface to use object and do some internal type checks prior to
using the thing). Note that there is a cost to this ¨C you will pay by
giving up some simplicity.

I don¡¯t think generics have anything to do with this. In .NET all types
must be fully defined at compilation time, generics is a run-time
mechanism, too late for a ¡°compilation firewall¡±.

Thanks.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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