Arrow 之 Builder

AppendArraySlice

AppendArraySlice 这个接口，目前每个 builder 都会有.

所以最终的copy 实现是在builder_primitive.h

NumericBuilder 之 AppendArraySlice

arrow/cpp/src/arrow/array/builder_primitive.h

  Status AppendArraySlice(const ArrayData& array, int64_t offset,
                          int64_t length) override {
    return AppendValues(array.GetValues<value_type>(1) + offset, length,
                        array.GetValues<uint8_t>(0, 0), array.offset + offset);
  }

/// \brief Append a sequence of elements in one shot
  /// \param[in] values a contiguous C array of values
  /// \param[in] length the number of values to append
  /// \param[in] bitmap a validity bitmap to copy (may be null)
  /// \param[in] bitmap_offset an offset into the validity bitmap
  /// \return Status
  Status AppendValues(const value_type* values, int64_t length, const uint8_t* bitmap,
                      int64_t bitmap_offset) {
    ARROW_RETURN_NOT_OK(Reserve(length));
    data_builder_.UnsafeAppend(values, length);
    // length_ is update by these
    ArrayBuilder::UnsafeAppendToBitmap(bitmap, bitmap_offset, length);
    return Status::OK();
  }

arrow/cpp/src/arrow/buffer_builder.h

void UnsafeAppend(const T* values, int64_t num_elements) {
    bytes_builder_.UnsafeAppend(reinterpret_cast<const uint8_t*>(values),
                                num_elements * sizeof(T));
  }

// Unsafe methods don't check existing size
  void UnsafeAppend(const void* data, const int64_t length) {
    memcpy(data_ + size_, data, static_cast<size_t>(length));
    size_ += length;
  }