Add technical docs on generic interfaces codegen #1989
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jevansaks
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Jun 9, 2025
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| This type derives from `WindowsRuntimeObject`, which provides all the usual support for IDIC, generated COM interfaces, and more. If needed, these RCW types (one per generic interface) can also contain additional state necessary to properly map the Windows Runtime interface behavior to the managed one. This is the case for `IEnumerator<T>`, which is slightly different than `IIterator<T>`, for instance. | ||
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| Next, an interface is needed for each "Methods" implementation, for each generic interface. For `IIterator<T>`, it looks like this: |
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I was mostly with you until this point. "An interface is needed" -- why? How does this connect to the scenarios above? I assume there's some general-purpose C#/WinRT machinery that is trying to reach out for this, but when/where?
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| This is conceptually similar to `IWindowsRuntimeComWrappersCallback` (which is used for delegates and sealed runtime class names), with the main difference being that it is specialized for unsealed types (and interfaces). In this case, implementations need to know the runtime class name of the native object, to determine whether they can marshal it via the fast path using a statically visible RCW type (see below), or whether they should fallback to the logic to marshal arbitrary opaque object that is used when no static type information is available (which involves going through the interop type lookup to get the marshalling info, etc.). |
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Pretend I don't know anything about the current C#/WinRT implementation in this regard. What do I need to know/care about to evaluate this proposal? :)
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This PR adds docs explaining in detail all codegen to handle generic collection interfaces in CsWinRT 3.0.