25 template <class T> struct Span {  struct
26     Span() : begin_(nullptr), end_(nullptr) {}  in Span()  function
27     template <size_t N> Span(T (&a)[N]) : begin_(&a[0]), end_(&a[N]) {}  in Span()  function
28     template <class I> Span(I begin, I end) : begin_(&*begin), end_(&*end) {}  in Span()  argument
29     template <class I> Span(I begin, size_t size) : begin_(&*begin), end_(&begin[size]) {}  in Span()  argument
31     T* data() { return begin_; }  in data()
32     const T* data() const { return begin_; }  in data()
33     T* begin() { return begin_; }  in begin()
34     T* end() { return end_; }  in end()
35     const T* begin() const { return begin_; }  in begin()
36     const T* end() const { return end_; }  in end()
37     size_t size() const { return end_ - begin_; }  in size()
43     T* end_;