when is doGenCode called?

[Koert Kuipers <ko...@tresata.com>]

hello all,
i am trying to add an Expression to catalyst.

my Expression compiles fine and has:

override def eval(input: InternalRow): Any = ...

override def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = ...

it also seems to run fine. but i only ever see eval get called. how do i
tell spark to use doGenCode instead of eval?

thanks! koert