On Wed, Aug 10, 2022 at 6:04 PM Martin Jambor <mjam...@suse.cz> wrote: > > 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.
We could alternatively add length in addition to size (and maybe size to vec<> if std::vector has size but not length) with a comment deprecating the "non-standard" variant? Richard. > > Thanks, > > Martin >