Blueprint Interface Function with input AND output - bug or evil feature?

Hey guys!
I’m trying to pass some data from one BP to another via BP Interface.
But when I add output to function in BP Interface - I can’t add event for this function anymore.
Without output and with only input it works correctly
But what the point of input, you can’t pass this data out?

Oh, seems like input works also as an output. Weird o.o

Yeah I found interfaces a bit counter intuitive as well.

Okay, this was answered on answer hub a few days ago.

To sum it up:

  1. For any interface function that does NOT have output, UE4 would treat it as a Event, since there are no potential dependency that could depend on the result of its execution, thus could go into the event queue.
  2. any interface function that has an output, because what implied to use the output value, it would be treated as a function and inherit the limitation of a function, and must return right away.