Why do we need throw null in src/libraries/System.Collections/ref and that folder in general?

[B1Z0N]

Why do we need that?

[EgorBo]

/ref is auto-generated tiny facades. They are used in order to produce small-sized referenced assemblies needed for faster compilation - they're not used during the actual application run.

throw null is basically a universal way to implement a method body - it's never invoked in practice.

[B1Z0N]

Oh, I see, the Libs.Ref subset triggers RefOnly mode and it uses ref instead of src. Just two more questions:

1. What generates this ref directory?
2. In what case I'd want to use this RefOnly mode, what scenario?

Thanks a lot for your answer!

[bartonjs]

https://docs.microsoft.com/en-us/dotnet/standard/assembly/reference-assemblies

Two reasons that we use them:

• It provides a single file that shows us just the public API revision history.
• It helps us (with additional tooling) make sure that any library that builds with OS-specific flavors all share the same public API -- the public API that we defined in the reference assembly.