When I have a lambda used as an single-method interface, and that interface method takes 2 parameters, the lambda needs to 2 params also. If I don't use one of the params in a particular instance, the compiler warns me that the param is unused, but of course I cannot delete the param. Is there a workaround, or some way to indicate to the compiler what's going on?

The IDE is suggesting to rename the parameter to

_

. You should press Alt + Enter to see available suggestions.