How to extend or modify already published COM object interface in C++

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I have request to add new method in already published COM object

interface ItestAutomationServer : IDispatch

add one more out parameter in existing method of following interface

interface ISinkNewAutomationTest : IUnknown

any one knows how to solve this?

What I have tried:

I have inherited as following and added new method

interface ItestAutomationServer1 : ItestAutomationServer

I have inherited as following and added new method with that extra parameter

interface ISinkNewAutomationTest1 : ISinkNewAutomationTest

Posted 12-Feb-19 2:02am

neetagaikwad

Updated 12-Feb-19 12:59pm

Rick York

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F-ES Sitecore 12-Feb-19 10:10am

Can't help with the specifics on implementation, but this is usually done with interface forwarding. If you add a param to an existing method then it'll break the objects already compiled against it. So instead you create a new method on a new interface that has the relevant params and leave the only interface in place. You change the old interface to call the new interface so old code continues to work, and if the interface is registered correctly any code compiled against the new interface will see the additional parameter.

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KarstenK · Answer 1 · 2019-02-12T05:08:00

Normally it is done via a new version of the interface. Than the implemenation is asking for the needed interface and its version. Than use the QueryInterfacemethod to get the supported interface. See the example how to support different intefaces.

Inheritance is a good idea, because it ensures compatibility.

CPallini · Answer 2 · 2019-02-12T12:59:00

COM interfaces are immutable you shall not try to change them. You have to create new interfaces. From the documentation[^]:

COM interfaces are immutable. You cannot define a new version of an old interface and give it the same identifier. Adding or removing methods of an interface or changing semantics creates a new interface, not a new version of an old interface.

How to extend or modify already published COM object interface in C++

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