P2325R3 Views should not be required to be default constructible

Also fixes LWG3479.

 - Conflicts addressed by assuming P2328R0 was applied.
 - Used non-propagating-cache for split_view.

Author: jensmaurer

source/containers.tex

@@ -10866,8 +10866,7 @@
     class span;
 
   template<class ElementType, size_t Extent>
-    inline constexpr bool ranges::enable_view<span<ElementType, Extent>> =
-      Extent == 0 || Extent == dynamic_extent;
+    inline constexpr bool ranges::enable_view<span<ElementType, Extent>> = true;
   template<class ElementType, size_t Extent>
     inline constexpr bool ranges::enable_borrowed_range<span<ElementType, Extent>> = true;
 

source/iterators.tex

@@ -1319,7 +1319,7 @@
 
 template<class I>
   concept @\deflibconcept{weakly_incrementable}@ =
-    @\libconcept{default_initializable}@<I> && @\libconcept{movable}@<I> &&
+    @\libconcept{movable}@<I> &&
     requires(I i) {
       typename iter_difference_t<I>;
       requires @\exposid{is-signed-integer-like}@<iter_difference_t<I>>;
@@ -3721,7 +3721,7 @@
   template<class Container>
   class back_insert_iterator {
   protected:
-    Container* container = nullptr;
+    Container* container;
 
   public:
     using iterator_category = output_iterator_tag;
@@ -3731,7 +3731,6 @@
     using reference         = void;
     using container_type    = Container;
 
-    constexpr back_insert_iterator() noexcept = default;
     constexpr explicit back_insert_iterator(Container& x);
     constexpr back_insert_iterator& operator=(const typename Container::value_type& value);
     constexpr back_insert_iterator& operator=(typename Container::value_type&& value);
@@ -3833,7 +3832,7 @@
   template<class Container>
   class front_insert_iterator {
   protected:
-    Container* container = nullptr;
+    Container* container;
 
   public:
     using iterator_category = output_iterator_tag;
@@ -3843,7 +3842,6 @@
     using reference         = void;
     using container_type    = Container;
 
-    constexpr front_insert_iterator() noexcept = default;
     constexpr explicit front_insert_iterator(Container& x);
     constexpr front_insert_iterator& operator=(const typename Container::value_type& value);
     constexpr front_insert_iterator& operator=(typename Container::value_type&& value);
@@ -3945,8 +3943,8 @@
   template<class Container>
   class insert_iterator {
   protected:
-    Container* container = nullptr;
-    ranges::iterator_t<Container> iter = ranges::iterator_t<Container>();
+    Container* container;
+    ranges::iterator_t<Container> iter;
 
   public:
     using iterator_category = output_iterator_tag;
@@ -3956,7 +3954,6 @@
     using reference         = void;
     using container_type    = Container;
 
-    insert_iterator() = default;
     constexpr insert_iterator(Container& x, ranges::iterator_t<Container> i);
     constexpr insert_iterator& operator=(const typename Container::value_type& value);
     constexpr insert_iterator& operator=(typename Container::value_type&& value);
@@ -4732,7 +4729,7 @@
     requires (!@\libconcept{same_as}@<I, S> && @\libconcept{copyable}@<I>)
   class common_iterator {
   public:
-    constexpr common_iterator() = default;
+    constexpr common_iterator() requires @\libconcept{default_initializable}@<I> = default;
     constexpr common_iterator(I i);
     constexpr common_iterator(S s);
     template<class I2, class S2>
@@ -5200,7 +5197,7 @@
                         // if the \grammarterm{qualified-id} \tcode{I::iterator_concept} is valid and denotes a type
     using iterator_category = typename I::iterator_category;    // present only
                         // if the \grammarterm{qualified-id} \tcode{I::iterator_category} is valid and denotes a type
-    constexpr counted_iterator() = default;
+    constexpr counted_iterator() requires @\libconcept{default_initializable}@<I> = default;
     constexpr counted_iterator(I x, iter_difference_t<I> n);
     template<class I2>
       requires @\libconcept{convertible_to}@<const I2&, I>
@@ -6028,7 +6025,6 @@
     using traits_type       = traits;
     using ostream_type      = basic_ostream<charT,traits>;
 
-    constexpr ostream_iterator() noexcept = default;
     ostream_iterator(ostream_type& s);
     ostream_iterator(ostream_type& s, const charT* delimiter);
     ostream_iterator(const ostream_iterator& x);
@@ -6041,8 +6037,8 @@
     ostream_iterator& operator++(int);
 
   private:
-    basic_ostream<charT,traits>* out_stream = nullptr;          // \expos
-    const charT* delim = nullptr;                               // \expos
+    basic_ostream<charT,traits>* out_stream;            // \expos
+    const charT* delim;                                 // \expos
   };
 }
 \end{codeblock}
@@ -6390,7 +6386,6 @@
     using streambuf_type    = basic_streambuf<charT,traits>;
     using ostream_type      = basic_ostream<charT,traits>;
 
-    constexpr ostreambuf_iterator() noexcept = default;
     ostreambuf_iterator(ostream_type& s) noexcept;
     ostreambuf_iterator(streambuf_type* s) noexcept;
     ostreambuf_iterator& operator=(charT c);
@@ -6401,7 +6396,7 @@
     bool failed() const noexcept;
 
   private:
-    streambuf_type* sbuf_ = nullptr;    // \expos
+    streambuf_type* sbuf_;              // \expos
   };
 }
 \end{codeblock}