variants.nim

type
  TKind1 = enum TK1A, TK1B
  TKind2 = enum TK2A, TK2B
  TKind3 = enum TK3A, TK3B

  TK2 = object
    case kind: TKind2
    of TK2A: tk2_int: int
    of TK2B: tk2_string: string

  TK3 = object
    case kind: TKind3
    of TK3A: tk3_int: int
    of TK3B: tk3_string: string

  TK1 = object
    case kind: TKind1
    of TK1A:
      root1: int
      suba: TK2
    of TK1B:
      root2: string
      subb: TK3

when isMainModule:
  var test1, test2, test3, test4: TK1
  test1.kind = TK1A
  test1.suba.kind = TK2A
  test1.suba.tk2_int = 3
  test2.kind = TK1A
  test2.suba.kind = TK2B
  test2.suba.tk2_string = "3"
  test3.kind = TK1B
  test3.subb.kind = TK3A
  test3.subb.tk3_int = 3
  test4.kind = TK1B
  test4.subb.kind = TK3B
  test4.subb.tk3_string = "3"
  echo repr(test1)
  echo repr(test2)
  echo repr(test3)
  echo repr(test4)