A testcase does the following:
As is it fails on invoke size with an error Parameter object is already assigned. So it seems that list is not written as a single object into a pipe, but instead all objects from list written into a pipe one-by-one.
However, if this would true, we could use commands like length and foreach after invoke eAdapters, but these commands fail with an error:
Do not know how to box value of type 'org.eclipse.emf.common.notify.impl.BasicNotifierImpl$EAdapterList'