P1227R2 Signed ssize() functions, unsigned size() functions

Author: jensmaurer

source/containers.tex

@@ -10250,23 +10250,19 @@
 \begin{codeblock}
 namespace std {
   // constants
-  inline constexpr ptrdiff_t dynamic_extent = -1;
+  inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
 
   // \ref{views.span}, class template span
-  template<class ElementType, ptrdiff_t Extent = dynamic_extent>
+  template<class ElementType, size_t Extent = dynamic_extent>
     class span;
 
   // \ref{span.objectrep}, views of object representation
-  template<class ElementType, ptrdiff_t Extent>
-    span<const byte,
-         Extent == dynamic_extent ? dynamic_extent
-                                  : static_cast<ptrdiff_t>(sizeof(ElementType)) * Extent>
+  template<class ElementType, size_t Extent>
+    span<const byte, Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
       as_bytes(span<ElementType, Extent> s) noexcept;
 
-  template<class ElementType, ptrdiff_t Extent>
-    span<byte,
-         Extent == dynamic_extent ? dynamic_extent
-                                  : static_cast<ptrdiff_t>(sizeof(ElementType)) * Extent>
+  template<class ElementType, size_t Extent>
+    span<byte, Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
       as_writable_bytes(span<ElementType, Extent> s) noexcept;
 }
 \end{codeblock}
@@ -10297,13 +10293,13 @@
 \indexlibrary{\idxcode{span}}%
 \begin{codeblock}
 namespace std {
-  template<class ElementType, ptrdiff_t Extent = dynamic_extent>
+  template<class ElementType, size_t Extent = dynamic_extent>
   class span {
   public:
     // constants and types
     using element_type = ElementType;
     using value_type = remove_cv_t<ElementType>;
-    using index_type = ptrdiff_t;
+    using index_type = size_t;
     using difference_type = ptrdiff_t;
     using pointer = element_type*;
     using reference = element_type&;
@@ -10328,19 +10324,19 @@
     template<class Container>
       constexpr span(const Container& cont);
     constexpr span(const span& other) noexcept = default;
-    template<class OtherElementType, ptrdiff_t OtherExtent>
+    template<class OtherElementType, size_t OtherExtent>
       constexpr span(const span<OtherElementType, OtherExtent>& s) noexcept;
 
     ~span() noexcept = default;
 
     constexpr span& operator=(const span& other) noexcept = default;
 
     // \ref{span.sub}, subviews
-    template<ptrdiff_t Count>
+    template<size_t Count>
       constexpr span<element_type, Count> first() const;
-    template<ptrdiff_t Count>
+    template<size_t Count>
       constexpr span<element_type, Count> last() const;
-    template<ptrdiff_t Offset, ptrdiff_t Count = dynamic_extent>
+    template<size_t Offset, size_t Count = dynamic_extent>
       constexpr span<element_type, @\seebelow@> subspan() const;
 
     constexpr span<element_type, dynamic_extent> first(index_type count) const;
@@ -10393,10 +10389,6 @@
 \tcode{ElementType} is required to be
 a complete object type that is not an abstract class type.
 
-\pnum
-If \tcode{Extent} is negative and not equal to \tcode{dynamic_extent},
-the program is ill-formed.
-
 \rSec3[span.cons]{Constructors, copy, and assignment}
 
 \indexlibrary{\idxcode{span}!constructor}%
@@ -10533,7 +10525,7 @@
 
 \indexlibrary{\idxcode{span}!constructor}%
 \begin{itemdecl}
-template<class OtherElementType, ptrdiff_t OtherExtent>
+template<class OtherElementType, size_t OtherExtent>
   constexpr span(const span<OtherElementType, OtherExtent>& s) noexcept;
 \end{itemdecl}
 \begin{itemdescr}
@@ -10569,12 +10561,12 @@
 
 \indexlibrarymember{span}{first}%
 \begin{itemdecl}
-template<ptrdiff_t Count> constexpr span<element_type, Count> first() const;
+template<size_t Count> constexpr span<element_type, Count> first() const;
 \end{itemdecl}
 \begin{itemdescr}
 \pnum
 \requires
-\tcode{0 <= Count \&\& Count <= size()}.
+\tcode{Count <= size()}.
 
 \pnum
 \effects
@@ -10583,12 +10575,12 @@
 
 \indexlibrarymember{span}{last}%
 \begin{itemdecl}
-template<ptrdiff_t Count> constexpr span<element_type, Count> last() const;
+template<size_t Count> constexpr span<element_type, Count> last() const;
 \end{itemdecl}
 \begin{itemdescr}
 \pnum
 \requires
-\tcode{0 <= Count \&\& Count <= size()}.
+\tcode{Count <= size()}.
 
 \pnum
 \effects
@@ -10597,15 +10589,14 @@
 
 \indexlibrarymember{span}{subspan}%
 \begin{itemdecl}
-template<ptrdiff_t Offset, ptrdiff_t Count = dynamic_extent>
+template<size_t Offset, size_t Count = dynamic_extent>
   constexpr span<element_type, @\seebelow@> subspan() const;
 \end{itemdecl}
 \begin{itemdescr}
 \pnum
 \requires
 \begin{codeblock}
-(0 <= Offset && Offset <= size())
-&& (Count == dynamic_extent || Count >= 0 && Offset + Count <= size())
+Offset <= size() && (Count == dynamic_extent || Offset + Count <= size())
 \end{codeblock}
 
 \pnum
@@ -10633,7 +10624,7 @@
 \begin{itemdescr}
 \pnum
 \requires
-\tcode{0 <= count \&\& count <= size()}.
+\tcode{count <= size()}.
 
 \pnum
 \effects
@@ -10647,7 +10638,7 @@
 \begin{itemdescr}
 \pnum
 \requires
-\tcode{0 <= count 0 \&\& count <= size()}.
+\tcode{count <= size()}.
 
 \pnum
 \effects
@@ -10663,8 +10654,7 @@
 \pnum
 \requires
 \begin{codeblock}
-(0 <= offset && offset <= size())
-&& (count == dynamic_extent || count >= 0 && offset + count <= size())
+offset <= size() && (count == dynamic_extent || offset + count <= size())
 \end{codeblock}
 
 \pnum
@@ -10718,7 +10708,7 @@
 \begin{itemdescr}
 \pnum
 \requires
-\tcode{0 <= idx \&\& idx < size()}.
+\tcode{idx < size()}.
 
 \pnum
 \effects
@@ -10826,10 +10816,8 @@
 
 \indexlibrary{\idxcode{as_bytes}}%
 \begin{itemdecl}
-template<class ElementType, ptrdiff_t Extent>
-  span<const byte,
-       Extent == dynamic_extent ? dynamic_extent
-                                : static_cast<ptrdiff_t>(sizeof(ElementType)) * Extent>
+template<class ElementType, size_t Extent>
+  span<const byte, Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
     as_bytes(span<ElementType, Extent> s) noexcept;
 \end{itemdecl}
 \begin{itemdescr}
@@ -10840,10 +10828,8 @@
 
 \indexlibrary{\idxcode{as_writable_bytes}}%
 \begin{itemdecl}
-template<class ElementType, ptrdiff_t Extent>
-  span<byte,
-       Extent == dynamic_extent ? dynamic_extent
-                                : static_cast<ptrdiff_t>(sizeof(ElementType)) * Extent>
+template<class ElementType, size_t Extent>
+  span<byte, Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
     as_writable_bytes(span<ElementType, Extent> s) noexcept;
 \end{itemdecl}
 \begin{itemdescr}

source/iterators.tex

@@ -438,6 +438,9 @@
 
   template<class C> constexpr auto size(const C& c) -> decltype(c.size());
   template<class T, size_t N> constexpr size_t size(const T (&array)[N]) noexcept;
+  template<class C> constexpr auto ssize(const C& c)
+    -> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;
+  template<class T, ptrdiff_t N> constexpr ptrdiff_t ssize(const T (&array)[N]) noexcept;
   template<class C> [[nodiscard]] constexpr auto empty(const C& c) -> decltype(c.empty());
   template<class T, size_t N> [[nodiscard]] constexpr bool empty(const T (&array)[N]) noexcept;
   template<class E> [[nodiscard]] constexpr bool empty(initializer_list<E> il) noexcept;
@@ -6520,6 +6523,28 @@
 \pnum \returns \tcode{N}.
 \end{itemdescr}
 
+\indexlibrary{\idxcode{ssize(C\& c)}}%
+\begin{itemdecl}
+template <class C>
+constexpr auto ssize(const C& c)
+    -> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;
+\end{itemdecl}
+\begin{itemdescr}
+\pnum \returns
+\begin{codeblock}
+static_cast<common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>>(c.size())
+\end{codeblock}
+\end{itemdescr}
+
+\indexlibrary{\idxcode{ssize(T (\&array)[N])}}%
+\begin{itemdecl}
+template <class T, ptrdiff_t N>
+constexpr ptrdiff_t ssize(const T (&array)[N]) noexcept;
+\end{itemdecl}
+\begin{itemdescr}
+\pnum \returns \tcode{N}.
+\end{itemdescr}
+
 \indexlibrary{\idxcode{empty(C\& c)}}%
 \begin{itemdecl}
 template<class C> [[nodiscard]] constexpr auto empty(const C& c) -> decltype(c.empty());