[Issue 12607] Document that IUnknown classes must mark toString with extern(D) when overriding it

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12607

--- Comment #3 from Andrej Mitrovic <andrej.mitrovich at gmail.com> ---
The only problem is, how do you call toString via an IUnknown interface? I need
it to implement better support for formatting COM objects, see Issue 11175.

IUnknown doesn't declare toString, but if you cast an IUnknown interface to
object you get back null.

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