Method subspan

external/include/fstd/span.h:450–456

    TCB_SPAN_CONSTEXPR11 span<element_type, dynamic_extent>
    subspan(size_type offset, size_type count = dynamic_extent) const
    {
        TCB_SPAN_EXPECT(offset <= size() &&
                        (count == dynamic_extent || offset + count <= size()));
        return {data() + offset,
                count == dynamic_extent ? size() - offset : count};
    }

    // [span.obs], span observers
    constexpr size_type size() const noexcept { return storage_.size; }