Misleading example in .NET 5 design document

[Flavien]

There seems to be a confusing example (potentially wrong?) in the document about Target Framework Names in .NET 5. This is the example about using TFMs to vary implementation.

It says:

Ida is working on a Xamarin Forms application that supports Android, iOS, and Windows. Her application needs GPS information, but only a very limited set. Since there is no portable GPS API, she writes her own little abstraction library using multi-targeting.

By doing so, she's able to encapsulate the GPS access without having to multi-target her entire application, just this one area.

So I imagine there is a XamarinApplication project targeting net5.0 (it says "without having to multi-target her entire application") and a XamarinGps library targeting net5.0-ios;net5.0-android;net5.0-windows;net5.0 of which the implementation is outlined in the example.

The problem is that since XamarinApplication is not using multitargeting and targets just net5.0, the version of XamarinGps that will be used is the net5.0 one, and that version has no implementation (just throw new PlatformNotSupportedException()).

Unless I misunderstand something, it will not work unless XamarinApplication also targets net5.0-ios;net5.0-android;net5.0-windows (in which case the platform specific implementations will be used).

If Ida wants to avoid multitargeting in XamarinApplication, it sounds like she should be using runtime identifiers, not TFMs.

Am I missing something or is the example misleading?

cc: @terrajobst since he's the author.

[akoeplinger]

Yes I think you're right, the main application would need to multi-target as well.