    const_iterator(const char *charPtr, const char16_t *char16Ptr)
        : charPtr_(charPtr), char16Ptr_(char16Ptr) {
      assert(
          ((!charPtr_) ^ (!char16Ptr_)) &&
          "Must provide one of char or char16 pointer");
    }
    const_iterator(const char *charPtr, const char16_t *char16Ptr)
        : charPtr_(charPtr), char16Ptr_(char16Ptr) {
      assert(
          ((!charPtr_) ^ (!char16Ptr_)) &&
          "Must provide one of char or char16 pointer");
    }