template<std::size_t Extent, std::size_t Offset, std::size_t Count>
struct xgboost::common::detail::ExtentValue< Extent, Offset, Count >
The extent E of the span returned by subspan is determined as follows:
- If Count is not dynamic_extent, Count;
- Otherwise, if Extent is not dynamic_extent, Extent - Offset;
- Otherwise, dynamic_extent.