(1) Before answering the question, I'd argue that this is one of many C++
defects you really ought to avoid. [I'm not alone in
this.](https://stackoverflow.com/questions/2986891/how-to-publicly-inherit-from-a-base-class-but-make-some-of-public-methods-from-t)
If a class inherits behavior from its parent, it ought not attempt to undefine
that parent's behavior. Unless you're building trivial software, you _will_
break something sooner or later. If you don't believe me, pay special attention
to the last sentence of the accepted answer on that page.
(2) I think the kludge below does something like what you want, but it really
is a kludge (I am not a Nim expert). First, a module to define the types:
type
Preant* = ref object of RootObj
proc call*(this: Preant) =
echo "Call Preant"
type
Child* = ref object of Preant
proc call*(this: Child) {.compileTime.} = discard
Run
Now a module that attempts to use them:
import preant
let c = new Child
let p: Preant = c
c.call() # does not compile if this is left uncommented
p.call() # compiles and runs, calling p's call()
Run
Output with `c.call()` uncommented:
$ nim c use_preant.nim
Hint: used config file '.choosenim/toolchains/nim-1.0.2/config/nim.cfg'
[Conf]
Hint: system [Processing]
Hint: widestrs [Processing]
Hint: io [Processing]
Hint: use_preant [Processing]
Hint: preant [Processing]
CC: stdlib_system.nim
CC: preant.nim
CC: use_preant.nim
Hint: [Link]
Hint: operation successful (14420 lines compiled; 0.523 sec total;
15.992MiB peakmem; Debug Build) [SuccessX]
$ ./use_preant
Call Preant
Run
Output with `c.call()` commented:
$ nim c use_preant.nim
Hint: used config file '.choosenim/toolchains/nim-1.0.2/config/nim.cfg'
[Conf]
Hint: system [Processing]
Hint: widestrs [Processing]
Hint: io [Processing]
Hint: use_preant [Processing]
Hint: preant [Processing]
use_preant.nim(6, 3) Error: request to generate code for .compileTime proc:
call
Run
I'm sure someone better versed in Nim will come along with a more elegant
answer, and maybe someone will berate me for berating C++, and that's OK; I'll
learn. Until then, I maintain that you really shouldn't go down this road to
start with.
