Suggestion to add callbacks or extension points to CppWinRT property implementations

[amtopel]

I was wondering if it would be possible to add callback support or extension points to the CppWinRT property implementation classes (like single_threaded_notifying_property, etc.).

So, for example, you could execute some code when a property is updated.

Perhaps this could be done using virtual methods or CRTP, although I'm not sure what the best implementation would be. Thanks for any thoughts or input.

[sylveon]

You can always just subscribe to your own NotifyPropertyChanged event.

[amtopel]

Oh yeah, good point. That’s not a bad idea. Thanks for pointing that out.

[jonwis]

I looked at this while adding the initial support. There's no (good) way to do this without either a bunch of boilerplate copypasta, resorting to macros, or having every member property be at least one pointer larger than the data it's storing. IIRC @asklar and @dmachaj also had thoughts about this. The problem is in trying to find the "containing record" for a member field, enabling a call-to-method step.

What these types don't support well is Windows' "everything is MTA ready by default, unless you're by necessity thread-affine." So what I wanted was an "acquire this srwlock for read/write, update the field, etc." I had https://godbolt.org/z/vsMKohjaK working (or something like it) but it was going to cost that extra "this" pointer, so I didn't complete it.

You could propose something similar - an explicit larger (but more useful?) type people can opt-in-to.

If someone has a clever "find enclosing from self" helper, please let me know.

[sylveon]

When using crtp, you can do static_cast<Derived*>(this)