P1523R1 Views and Size Types

Fixes #3034.

Author: Dawn Perchik

source/ranges.tex

@@ -589,10 +589,10 @@
   \end{itemize}
 
 \item
-  Otherwise, \tcode{(ranges::end(E) - ranges::begin(E))}
+  Otherwise, \tcode{\placeholdernc{make-unsigned-like}(ranges::end(E) - ranges::begin(E))}\iref{range.subrange}
   if it is a valid expression and
   the types \tcode{I} and \tcode{S} of \tcode{ranges::begin(E)} and
-  \tcode{ranges::end(E)} (respectively) model both
+  \tcode{ranges::end(E)} (respectively) model both\hfill\break %avoid overfull
   \tcode{SizedSentinel<S, I>}\iref{iterator.concept.sizedsentinel} and
   \tcode{Forward\-Iterator<I>}.
   However, \tcode{E} is evaluated only once.
@@ -1209,7 +1209,7 @@
 \begin{codeblock}
 namespace std::ranges {
   template<class T>
-    concept @\placeholdernc{pair-like}@ =                                 // \expos
+    concept @\placeholdernc{pair-like}@ =                                    // \expos
       !is_reference_v<T> && requires(T t) {
         typename tuple_size<T>::type;   // ensures \tcode{tuple_size<T>} is complete
         requires DerivedFrom<tuple_size<T>, integral_constant<size_t, 2>>;
@@ -1220,19 +1220,19 @@
       };
 
   template<class T, class U, class V>
-    concept @\placeholdernc{pair-like-convertible-to}@ =                  // \expos
+    concept @\placeholdernc{pair-like-convertible-to}@ =                     // \expos
       !Range<T> && @\placeholder{pair-like}@<remove_reference_t<T>> &&
       requires(T&& t) {
         { get<0>(std::forward<T>(t)) } -> ConvertibleTo<U>;
         { get<1>(std::forward<T>(t)) } -> ConvertibleTo<V>;
       };
 
   template<class T, class U, class V>
-    concept @\placeholdernc{pair-like-convertible-from}@ =                // \expos
+    concept @\placeholdernc{pair-like-convertible-from}@ =                   // \expos
       !Range<T> && @\placeholdernc{pair-like}@<T> && Constructible<T, U, V>;
 
   template<class T>
-    concept @\placeholdernc{iterator-sentinel-pair}@ =                    // \expos
+    concept @\placeholdernc{iterator-sentinel-pair}@ =                       // \expos
       !Range<T> && @\placeholdernc{pair-like}@<T> &&
       Sentinel<tuple_element_t<1, T>, tuple_element_t<0, T>>;
 
@@ -1241,18 +1241,18 @@
     requires (K == subrange_kind::sized || !SizedSentinel<S, I>)
   class subrange : public view_interface<subrange<I, S, K>> {
   private:
-    static constexpr bool StoreSize =                   // \expos
+    static constexpr bool StoreSize =                      // \expos
       K == subrange_kind::sized && !SizedSentinel<S, I>;
-    I begin_ = I();                                     // \expos
-    S end_ = S();                                       // \expos
-    iter_difference_t<I> size_ = 0;                     // \expos; present only
-                                                        // when \tcode{StoreSize} is \tcode{true}
+    I begin_ = I();                                        // \expos
+    S end_ = S();                                          // \expos
+    @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>) size_ = 0;  // \expos; present only
+                                                           // when \tcode{StoreSize} is \tcode{true}
   public:
     subrange() = default;
 
     constexpr subrange(I i, S s) requires (!StoreSize);
 
-    constexpr subrange(I i, S s, iter_difference_t<I> n)
+    constexpr subrange(I i, S s, @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>) n)
       requires (K == subrange_kind::sized);
 
     template<@\placeholdernc{not-same-as}@<subrange> R>
@@ -1262,7 +1262,7 @@
 
     template<@\placeholdernc{forwarding-range}@ R>
       requires ConvertibleTo<iterator_t<R>, I> && ConvertibleTo<sentinel_t<R>, S>
-    constexpr subrange(R&& r, iter_difference_t<I> n)
+    constexpr subrange(R&& r, @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>) n)
       requires (K == subrange_kind::sized)
         : subrange{ranges::begin(r), ranges::end(r), n}
     {}
@@ -1275,7 +1275,7 @@
     {}
 
     template<@\placeholdernc{pair-like-convertible-to}@<I, S> PairLike>
-    constexpr subrange(PairLike&& r, iter_difference_t<I> n)
+    constexpr subrange(PairLike&& r, @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>) n)
       requires (K == subrange_kind::sized)
       : subrange{std::get<0>(std::forward<PairLike>(r)),
                  std::get<1>(std::forward<PairLike>(r)), n}
@@ -1289,7 +1289,7 @@
     constexpr S end() const;
 
     constexpr bool empty() const;
-    constexpr iter_difference_t<I> size() const
+    constexpr @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>) size() const
       requires (K == subrange_kind::sized);
 
     [[nodiscard]] constexpr subrange next(iter_difference_t<I> n = 1) const;
@@ -1302,13 +1302,14 @@
   };
 
   template<Iterator I, Sentinel<I> S>
-    subrange(I, S, iter_difference_t<I>) -> subrange<I, S, subrange_kind::sized>;
+    subrange(I, S, @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>)) ->
+      subrange<I, S, subrange_kind::sized>;
 
   template<@\placeholder{iterator-sentinel-pair}@ P>
     subrange(P) -> subrange<tuple_element_t<0, P>, tuple_element_t<1, P>>;
 
   template<@\placeholder{iterator-sentinel-pair}@ P>
-    subrange(P, iter_difference_t<tuple_element_t<0, P>>) ->
+    subrange(P, @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<tuple_element_t<0, P>>)) ->
       subrange<tuple_element_t<0, P>, tuple_element_t<1, P>, subrange_kind::sized>;
 
   template<@\placeholder{forwarding-range}@ R>
@@ -1318,7 +1319,7 @@
                  ? subrange_kind::sized : subrange_kind::unsized>;
 
   template<@\placeholder{forwarding-range}@ R>
-    subrange(R&&, range_difference_t<R>) ->
+    subrange(R&&, @\placeholdernc{make-unsigned-like-t}@(range_difference_t<R>)) ->
       subrange<iterator_t<R>, sentinel_t<R>, subrange_kind::sized>;
 
   template<size_t N, class I, class S, subrange_kind K>
@@ -1349,14 +1350,14 @@
 
 \indexlibrary{\idxcode{subrange}!\idxcode{subrange}}%
 \begin{itemdecl}
-constexpr subrange(I i, S s, iter_difference_t<I> n)
+constexpr subrange(I i, S s, @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>) n)
   requires (K == subrange_kind::sized);
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
 \expects \range{i}{s} is a valid range, and
-\tcode{n == ranges::distance(i, s)}.
+\tcode{n == \placeholdernc{make-unsigned-like}(ranges::distance(i, s))}.
 
 \pnum
 \effects Initializes \tcode{begin_} with \tcode{i} and \tcode{end_} with
@@ -1436,7 +1437,7 @@
 
 \indexlibrary{\idxcode{size}!\idxcode{subrange}}%
 \begin{itemdecl}
-constexpr iter_difference_t<I> size() const
+constexpr @\placeholdernc{make-unsigned-like-t}@(iter_difference_t<I>) size() const
   requires (K == subrange_kind::sized);
 \end{itemdecl}
 
@@ -1445,7 +1446,7 @@
 \effects
 \begin{itemize}
 \item If \tcode{StoreSize} is \tcode{true}, equivalent to: \tcode{return size_;}
-\item Otherwise, equivalent to: \tcode{return end_ - begin_;}
+\item Otherwise, equivalent to: \tcode{return \placeholdernc{make-unsigned-like-t}(end_ - begin_);}
 \end{itemize}
 \end{itemdescr}
 
@@ -1497,7 +1498,11 @@
 \begin{itemize}
 \item If \tcode{StoreSize} is \tcode{true},
 \begin{codeblock}
-size_ -= n - ranges::advance(begin_, n, end_);
+auto d = n - ranges::advance(begin_, n, end_);
+if (d >= 0)
+  size_ -= @\placeholdernc{make-unsigned-like}@(d);
+else
+  size_ += @\placeholdernc{make-unsigned-like}@(-d);
 return *this;
 \end{codeblock}
 \item Otherwise,
@@ -1605,7 +1610,7 @@
     static constexpr T* begin() noexcept { return nullptr; }
     static constexpr T* end() noexcept { return nullptr; }
     static constexpr T* data() noexcept { return nullptr; }
-    static constexpr ptrdiff_t size() noexcept { return 0; }
+    static constexpr size_t size() noexcept { return 0; }
     static constexpr bool empty() noexcept { return true; }
 
     friend constexpr T* begin(empty_view) noexcept { return nullptr; }
@@ -1652,7 +1657,7 @@
     constexpr const T* begin() const noexcept;
     constexpr T* end() noexcept;
     constexpr const T* end() const noexcept;
-    static constexpr ptrdiff_t size() noexcept;
+    static constexpr size_t size() noexcept;
     constexpr T* data() noexcept;
     constexpr const T* data() const noexcept;
   };
@@ -1715,7 +1720,7 @@
 
 \indexlibrary{\idxcode{size}!\idxcode{single_view}}%
 \begin{itemdecl}
-static constexpr ptrdiff_t size() noexcept;
+static constexpr size_t size() noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}