Merge 2019-11 LWG Motion 1

P1917R0 C++ Standard Library Issues to be moved in Belfast

Author: zygoloid

source/algorithms.tex

@@ -9328,13 +9328,16 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{U} be the value type of \tcode{decltype(first)}.
+
 \pnum
 \requires
 \begin{itemize}
 \item
   If \tcode{init} is provided,
   \tcode{T} shall be \oldconcept{MoveConstructible} (\tref{cpp17.moveconstructible});
-  otherwise, \tcode{ForwardIterator1}'s value type
+  otherwise, \tcode{U}
   shall be \oldconcept{MoveConstructible}.
 \item
   If \tcode{init} is provided, all of
@@ -9343,7 +9346,7 @@
   \tcode{binary_op(*first, *first)}
   shall be convertible to \tcode{T};
   otherwise, \tcode{binary_op(*first, *first)}
-  shall be convertible to \tcode{ForwardIterator1}'s value type.
+  shall be convertible to \tcode{U}.
 \item
   \tcode{binary_op} shall neither invalidate iterators or subranges,
   nor modify elements in
@@ -9491,13 +9494,16 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{U} be the value type of \tcode{decltype(first)}.
+
 \pnum
 \requires
 \begin{itemize}
 \item
   If \tcode{init} is provided, \tcode{T} shall be
   \oldconcept{MoveConstructible} (\tref{cpp17.moveconstructible});
-  otherwise, \tcode{ForwardIterator1}'s value type shall be
+  otherwise, \tcode{U} shall be
   \oldconcept{MoveConstructible}.
 \item
   If \tcode{init} is provided, all of
@@ -9508,7 +9514,7 @@
   \end{itemize}
   shall be convertible to \tcode{T};
   otherwise, \tcode{binary_op(unary_op(*first), unary_op(*first))}
-  shall be convertible to \tcode{ForwardIterator1}'s value type.
+  shall be convertible to \tcode{U}.
 \item
   Neither \tcode{unary_op} nor \tcode{binary_op} shall
   invalidate iterators or subranges, nor modify elements in

source/concepts.tex

@@ -736,9 +736,27 @@
 
 \begin{itemdecl}
 template<class T>
-  concept @\deflibconcept{default_constructible}@ = constructible_from<T>;
+  inline constexpr bool @\defexposconcept{is-default-initializable}@ = @\seebelow@;  // \expos
+
+template<class T>
+  concept @\deflibconcept{default_constructible}@ = constructible_from<T> &&
+                                  requires { T{}; } &&
+                                  @\exposconcept{is-default-initializable}@<T>;
 \end{itemdecl}
 
+\begin{itemdescr}
+\pnum
+For a type \tcode{T}, \tcode{\exposconcept{is-default-initializable}<T>} is \tcode{true}
+if and only if the variable definition
+\begin{codeblock}
+T t;
+\end{codeblock}
+is well-formed for some invented variable \tcode{t};
+otherwise it is \tcode{false}.
+Access checking is performed as if in a context unrelated to \tcode{T}.
+Only the validity of the immediate context of the variable initialization is considered.
+\end{itemdescr}
+
 \rSec2[concept.moveconstructible]{Concept \cname{move_constructible}}
 
 \begin{itemdecl}

source/containers.tex

@@ -10839,6 +10839,10 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\mandates
+\tcode{Count <= Extent} is \tcode{true}.
+
 \pnum
 \expects
 \tcode{Count <= size()} is \tcode{true}.
@@ -10854,6 +10858,10 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\mandates
+\tcode{Count <= Extent} is \tcode{true}.
+
 \pnum
 \expects
 \tcode{Count <= size()} is \tcode{true}.
@@ -10870,10 +10878,17 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\mandates
+\begin{codeblock}
+Offset <= Extent && (Count == dynamic_extent || Count <= Extent - Offset)
+\end{codeblock}
+is \tcode{true}.
+
 \pnum
 \expects
 \begin{codeblock}
-Offset <= size() && (Count == dynamic_extent || Offset + Count <= size())
+Offset <= size() && (Count == dynamic_extent || Count <= size() - Offset)
 \end{codeblock}
 is \tcode{true}.
 
@@ -10935,7 +10950,7 @@
 \pnum
 \expects
 \begin{codeblock}
-offset <= size() && (count == dynamic_extent || offset + count <= size())
+offset <= size() && (count == dynamic_extent || count <= size() - offset)
 \end{codeblock}
 is \tcode{true}.
 

source/iostreams.tex

@@ -10897,7 +10897,9 @@
     using streambuf_type = basic_streambuf<charT, traits>;
 
     // \ref{syncstream.syncbuf.cons}, construction and destruction
-    explicit basic_syncbuf(streambuf_type* obuf = nullptr)
+    basic_syncbuf()
+      : basic_syncbuf(nullptr) {}
+    explicit basic_syncbuf(streambuf_type* obuf)
       : basic_syncbuf(obuf, Allocator()) {}
     basic_syncbuf(streambuf_type*, const Allocator&);
     basic_syncbuf(basic_syncbuf&&);
@@ -12404,7 +12406,9 @@
 
 \pnum
 Functions taking template parameters named \tcode{Source}
-shall not participate in overload resolution unless either
+shall not participate in overload resolution unless
+\tcode{Source} denotes a type other than \tcode{path}, and
+either
 \begin{itemize}
 \item
 \tcode{Source} is a specialization of
@@ -13464,10 +13468,26 @@
 
 \pnum
 \effects
-If \tcode{root_name() != base.root_name()} is \tcode{true}
-or \tcode{is_absolute() != base.is_absolute()} is \tcode{true}
-or \tcode{!has_root_directory() \&\& base.has_root_directory()} is \tcode{true},
+If:
+\begin{itemize}
+\item
+\tcode{root_name() != base.root_name()} is \tcode{true}, or
+
+\item
+\tcode{is_absolute() != base.is_absolute()} is \tcode{true}, or
+
+\item
+\tcode{!has_root_directory() \&\& base.has_root_directory()} is \tcode{true}, or
+
+\item
+any \grammarterm{filename} in
+\tcode{relative_path()} or \tcode{base.relative_path()}
+can be interpreted as a \grammarterm{root-name},
+\end{itemize}
 returns \tcode{path()}.
+\begin{note}
+On a POSIX implementation, no \grammarterm{filename} in a \grammarterm{relative-path} is acceptable as a \grammarterm{root-name}.
+\end{note}
 Determines the first mismatched element of \tcode{*this} and \tcode{base}
 as if by:
 \begin{codeblock}

source/iterators.tex

@@ -655,11 +655,7 @@
 \indextext{iterator!constexpr}%
 Iterators are called \defn{constexpr iterators}
 if all operations provided to meet iterator category requirements
-are constexpr functions, except for
-\begin{itemize}
-\item a pseudo-destructor call\iref{expr.prim.id.dtor}, and
-\item the construction of an iterator with a singular value.
-\end{itemize}
+are constexpr functions.
 \begin{note}
 For example, the types ``pointer to \tcode{int}'' and
 \tcode{reverse_iterator<int*>} are constexpr iterators.
@@ -1783,7 +1779,7 @@
   \tcode{(a + D(x + y))} is equal to \tcode{((a + x) + y)}.
 \item \tcode{(a + D(0))} is equal to \tcode{a}.
 \item If \tcode{(a + D(n - 1))} is valid, then
-  \tcode{(a + n)} is equal to \tcode{++(a + D(n - 1))}.
+  \tcode{(a + n)} is equal to \tcode{[](I c)\{ return ++c; \}(a + D(n - 1))}.
 \item \tcode{(b += -n)} is equal to \tcode{a}.
 \item \tcode{(b -= n)} is equal to \tcode{a}.
 \item \tcode{addressof(b -= n)} is equal to \tcode{addressof(b)}.

source/ranges.tex

@@ -5200,7 +5200,8 @@
 namespace std::ranges {
   template<class V, class Pattern>
   template<bool Const>
-  struct split_view<V, Pattern>::outer_iterator<Const>::value_type {
+  struct split_view<V, Pattern>::outer_iterator<Const>::value_type
+    : view_interface<value_type> {
   private:
     outer_iterator i_ = outer_iterator();               // \expos
   public:

source/support.tex

@@ -554,7 +554,7 @@
   // \libheader{map}, \libheader{set}, \libheader{unordered_map}, \libheader{unordered_set}
 #define @\defnlibxname{cpp_lib_any}@                               201606L // also in \libheader{any}
 #define @\defnlibxname{cpp_lib_apply}@                             201603L // also in \libheader{tuple}
-#define @\defnlibxname{cpp_lib_array_constexpr}@                   201603L // also in \libheader{iterator}, \libheader{array}
+#define @\defnlibxname{cpp_lib_array_constexpr}@                   201803L // also in \libheader{iterator}, \libheader{array}
 #define @\defnlibxname{cpp_lib_as_const}@                          201510L // also in \libheader{utility}
 #define @\defnlibxname{cpp_lib_atomic_flag_test}@                  201907L // also in \libheader{atomic}
 #define @\defnlibxname{cpp_lib_atomic_is_always_lock_free}@        201603L // also in \libheader{atomic}
@@ -578,10 +578,10 @@
 #define @\defnlibxname{cpp_lib_concepts}@                          201806L // also in \libheader{concepts}
 #define @\defnlibxname{cpp_lib_constexpr}@                         201811L
   // also in any C++ library header from \tref{headers.cpp} or any C++ header for C library facilities from \tref{headers.cpp.c}
+#define @\defnlibxname{cpp_lib_constexpr_algorithms}@              201806L // also in \libheader{algorithm}
 #define @\defnlibxname{cpp_lib_constexpr_dynamic_alloc}@           201907L // also in \libheader{memory}
 #define @\defnlibxname{cpp_lib_constexpr_invoke}@                  201907L // also in \libheader{functional}
 #define @\defnlibxname{cpp_lib_constexpr_string}@                  201907L // also in \libheader{string}
-#define @\defnlibxname{cpp_lib_constexpr_swap_algorithms}@         201806L // also in \libheader{algorithm}
 #define @\defnlibxname{cpp_lib_constexpr_vector}@                  201907L // also in \libheader{vector}
 #define @\defnlibxname{cpp_lib_destroying_delete}@                 201806L // also in \libheader{new}
 #define @\defnlibxname{cpp_lib_enable_shared_from_this}@           201603L // also in \libheader{memory}
@@ -650,8 +650,9 @@
 #define @\defnlibxname{cpp_lib_shared_timed_mutex}@                201402L // also in \libheader{shared_mutex}
 #define @\defnlibxname{cpp_lib_source_location}@                   201907L // also in \libheader{source_location}
 #define @\defnlibxname{cpp_lib_spaceship}@                         201907L // also in \libheader{compare}
+#define @\defnlibxname{cpp_lib_span}@                              201902L // also in \libheader{span}
 #define @\defnlibxname{cpp_lib_string_udls}@                       201304L // also in \libheader{string}
-#define @\defnlibxname{cpp_lib_string_view}@                       201606L // also in \libheader{string}, \libheader{string_view}
+#define @\defnlibxname{cpp_lib_string_view}@                       201803L // also in \libheader{string}, \libheader{string_view}
 #define @\defnlibxname{cpp_lib_three_way_comparison}@              201711L // also in \libheader{compare}
 #define @\defnlibxname{cpp_lib_to_array}@                          201907L // also in \libheader{array}
 #define @\defnlibxname{cpp_lib_to_chars}@                          201611L // also in \libheader{charconv}