Crash on assigning actors implementing an interface to an array in Editor

Development Programming & Scripting UI
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1

Repro steps from a blank project:

  • create a blueprint interface BPI_Interface
  • create a blueprint class BP_InterfaceImplementation, child of Actor, implements BPI_Interface
  • create a blueprint class BP_InterfaceUser, child of Actor
  • add a variable of the type “array of BPI_Interface” to BP_InterfaceUser, mark it as Instance Editable
  • create an empty level and place BP_InterfaceUser and BP_InterfaceImplementation there
  • select BP_InterfaceUser, click “lock” on the details panel, click “+” to add a new item to the array, then drag and drop the BP_InterfaceImplementation from the World Outliner to the slot, and you get a crash

If you change BP_InterfaceUser’s variable type to be a single item of BPI_Interface, then the same actions will not crash the editor, but will fail to make the assignment.

This seems to be reproducable every time. I use UE 4.18, OS is Windows 7.

I attach a barebones project ready for the repro. Instead of BP_InterfaceUser there are BP_ArrayInterfaceUser with an array variable that can be used to get the crash, and BP_SingleInterfaceUser with a single item variable.

2

Doesn’t appear in 4.18.1