type
  BitVecKind = enum
    kArr, kVla, kSeq
  Units = SomeUnsignedInt

  BitVec3[arType: static BitVecKind, B: Units, S:static int] = object
    when arType is kArr:
      Base: array[S div (sizeof(B)  8) + int(S mod (sizeof(B)  8) != 0), B]
    when arType is kSeq:
      Base: seq[B]
    when arType is kVla:
      Base: VarLengthArray[B]
    size: int```