Thursday, June 07, 2018

.NET Framework assemblies can be called from .NET Core ?!

I was under the impression that .NET Framework can only reference .NET Framework assemblies and .NET Core can only reference .NET Core assemblies. After all, that's why .NET Standard appeared, so you can create assemblies that can be referenced from everywhere. However, one can actually reference .NET Framework assemblies from .NET Core (and not the other way around). Moreover, they work! How does that happen?

I chose a particular functionality that works only in Framework: AppDomain.CreateDomain. I've added it to a .NET 4.6 assembly, then referenced the assembly in a .NET Core program. And it compiled!! Does that mean that I can run whatever I want in .NET Core now?

The answer is no. When running the program, I get a PlatformNotSupportedException, meaning that the IL code is executed by .NET Core, but in its own context. It is basically a .NET Standard cheat. Personally, I don't like this, but I guess it's a measure to support adoption of the Core concept.

What goes on behind the scenes is that .NET Core implements .NET Standard, which can reference .NET Framework assemblies. For this to work you need .NET Core 2.0 and Visual Studio 2017 15.3 or higher.