TObjectPtr<T> with UInterface fails (can only be used with types derived from UObject) but... UInterface is derived from UObject

Development Programming & Scripting C++
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As the subject.

This was working in my project for the longest and then suddenly I start getting compile errors one day out of the blue.

The error is vague-monster because it does not point to the offending property, it points to a line of code in the unreal engine itself.

> static_assert failed: 'TObjectPtr<T> can only be used with types derived from UObject'

So I have to dig into my build stack and I see that its complaining about a line of code:
TObjectPtr<IMyInterface> MyVariable;

Digging into UInterface which my interface is derived from, I see clearly UInterface derives from UObject.

What gives here? Why did this suddenly start blowing up and what is the real problem? The interface IS derived from UObject.

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I can’t speak to why it “suddenly” started failing, but the assert that is happening is accurate.

Yes UMyInterface derives from UObject, but IMyInterface doesn’t.

If you want a variable like that you’d use TScriptInterface< IMyInterface >.

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Ah yes good catch. IMyInterface is different from the U object. Thank you.

When I say suddenly failed, this particular C++ file has not changed in seven months with successful builds going daily, and now all of a sudden its marked for fail on the above. The interface and the file itself have not changed at all in that time.

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Just had the same thing happen and it was driving me nuts, especially since the build error didn’t even go to the file that it was happening in…
I had my editor create a UInterface file for the first time as opposed to me creating it myself. I also now have an interface with a default implementation. Maybe this has something to do with it?

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