Ian Griffiths has written a very deep and informative post about what WinRT really is, and what is meant by all this "projection" vs "native" business. It's a great read, and you should dig in. Especially if you're an old COM hand, like myself.
I have seen a lot of important questions floating around lately (most notably from @kellabyte) that this post answers. But it takes a long time and many diversions before it gets there. So for those who don't have the time or the background to wade through Ian's post, I humbly present a TL;DR bullet list summary.
- WinRT appears to be the new Windows API. It is probably the next evolution of Win32.
- WinRT is native, and just as fast as native has always been.
- WinRT is rooted in the next evolution of COM, not .NET
- WinRT involves just as much indirection (and "inefficiency", compared to COM-less native code) as COM always has.
- WinRT "projections" are language-specific. For C++, they're native.
- WinRT projections do no more and no less than smooth over much of the API for consuming languages, putting a curtain around the pain and noise of working with COM and HRESULTs directly.
- WinRT projections are not the next .NET windowing framework. They do not replace WinForms, WPF, Silverlight.
I'll also add to this list my own prediction: We will probably not want to directly consume WinRT any more than we wanted to directly consume Win32. There will be value in a GUI framework to abstract that away, just as there always has been. I haven't heard any mention of the Metro-based successor to WPF/Silverlight, but I would expect one to be delivered with the next version of VS and .NET. I look forward to hearing more from DevDiv now that all the WinRT details are starting to trickle out.