Hello, I have one more question/comment about array_slice. Ever since I started to use it...
On Fri, Nov 13 2020, Richard Sandiford via Gcc-patches wrote: > A later patch wants to be able to pass around subarray views of an > existing array. The standard class to do that is std::span, but it's > a C++20 thing. This patch just adds a cut-down version of it. > > The intention is just to provide what's currently needed. > > gcc/ > * vec.h (array_slice): New class. > --- > gcc/vec.h | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 120 insertions(+) > > diff --git a/gcc/vec.h b/gcc/vec.h > index f02beddc975..7768de9f518 100644 > --- a/gcc/vec.h > +++ b/gcc/vec.h > @@ -2128,6 +2128,126 @@ release_vec_vec (vec<vec<T> > &vec) > vec.release (); > } > > +// Provide a subset of the std::span functionality. (We can't use std::span > +// itself because it's a C++20 feature.) > +// > +// In addition, provide an invalid value that is distinct from all valid > +// sequences (including the empty sequence). This can be used to return > +// failure without having to use std::optional. > +// > +// There is no operator bool because it would be ambiguous whether it is > +// testing for a valid value or an empty sequence. > +template<typename T> > +class array_slice > +{ > + template<typename OtherT> friend class array_slice; > + > +public: > + using value_type = T; > + using iterator = T *; > + using const_iterator = const T *; > + > + array_slice () : m_base (nullptr), m_size (0) {} > + > + template<typename OtherT> > + array_slice (array_slice<OtherT> other) > + : m_base (other.m_base), m_size (other.m_size) {} > + > + array_slice (iterator base, unsigned int size) > + : m_base (base), m_size (size) {} > + > + template<size_t N> > + array_slice (T (&array)[N]) : m_base (array), m_size (N) {} > + > + template<typename OtherT> > + array_slice (const vec<OtherT> &v) > + : m_base (v.address ()), m_size (v.length ()) {} > + > + iterator begin () { return m_base; } > + iterator end () { return m_base + m_size; } > + > + const_iterator begin () const { return m_base; } > + const_iterator end () const { return m_base + m_size; } > + > + value_type &front (); > + value_type &back (); > + value_type &operator[] (unsigned int i); > + > + const value_type &front () const; > + const value_type &back () const; > + const value_type &operator[] (unsigned int i) const; > + > + size_t size () const { return m_size; } ...this has been a constant source of compile errors, because vectors have length () and this is size (). I understand that the motivation was consistency with std::span, but do we really want to add another inconsistency with ourselves? Given that array_slice is not that much used yet, I believe we can still change to be consistent with vectors. I personally think we should but at the very least, if we keep it as it is, I'd like us to do so deliberately. Thanks, Martin