Merge 2021-06 LWG Motion 3

P2385R0 C++ Standard Library Issues to be moved in Virtual Plenary, June 2021

Author: tkoeppe

source/algorithms.tex

@@ -8618,23 +8618,23 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let $N$ be $\min(\tcode{e1 - b1}, \tcode{e2 - b2})$.
+Let $E(n)$ be \tcode{comp(*(b1 + $n$), *(b2 + $n$))}.
+
 \pnum
 \mandates
 \tcode{decltype(comp(*b1, *b2))} is a comparison category type.
 
 \pnum
-\effects
-Lexicographically compares two ranges and
-produces a result of the strongest applicable comparison category type.
-Equivalent to:
-\begin{codeblock}
-for ( ; b1 != e1 && b2 != e2; void(++b1), void(++b2) )
-  if (auto cmp = comp(*b1,*b2); cmp != 0)
-    return cmp;
-return b1 != e1 ? strong_ordering::greater :
-       b2 != e2 ? strong_ordering::less :
-                  strong_ordering::equal;
-\end{codeblock}
+\returns
+$E(i)$, where $i$ is the smallest integer in \range{0}{$N$}
+such that \tcode{$E(i)$ != 0} is \tcode{true}, or
+\tcode{(e1 - b1) <=> (e2 - b2)} if no such integer exists.
+
+\pnum
+\complexity
+At most $N$ applications of \tcode{comp}.
 \end{itemdescr}
 
 \indexlibraryglobal{lexicographical_compare_three_way}%
@@ -10831,7 +10831,8 @@
 \begin{itemdescr}
 \pnum
 \expects
-The objects in the array pointed to by \tcode{base} are of trivial type.
+For \tcode{qsort}, the objects in the array pointed to by \tcode{base}
+are of trivially copyable type.
 
 \pnum
 \effects

source/containers.tex

@@ -4651,6 +4651,12 @@
 arguments for a template parameter
 named \tcode{Predicate} or \tcode{BinaryPredicate}
 shall meet the corresponding requirements in \ref{algorithms.requirements}.
+The semantics of \tcode{i + n},
+where \tcode{i} is an iterator into the list and \tcode{n} is an integer,
+are the same as those of \tcode{next(i, n)}.
+The expression \tcode{i - n},
+where \tcode{i} is an iterator into the list and \tcode{n} is an integer,
+means an iterator \tcode{j} such that \tcode{j + n == i} is \tcode{true}.
 For \tcode{merge} and \tcode{sort},
 the definitions and requirements in \ref{alg.sorting} apply.
 
@@ -4784,16 +4790,24 @@
 \indexlibrarymember{unique}{forward_list}%
 \begin{itemdecl}
 size_type unique();
-template<class BinaryPredicate> size_type unique(BinaryPredicate pred);
+template<class BinaryPredicate> size_type unique(BinaryPredicate binary_pred);
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{binary_pred} be \tcode{equal_to<>\{\}} for the first overload.
+
+\pnum
+\expects
+\tcode{binary_pred} is an equivalence relation.
+
 \pnum
 \effects
 Erases all but the first element from every consecutive
-group of equal elements referred to by the iterator \tcode{i} in the range \range{first +
-1}{last} for which \tcode{*i == *(i-1)} (for the version with no arguments) or \tcode{pred(*i,
-*(i - 1))} (for the version with a predicate argument) holds.
+group of equivalent elements.
+That is, for a nonempty list, erases all elements referred to
+by the iterator \tcode{i} in the range \range{begin() + 1}{end()}
+for which \tcode{binary_pred(*i, *(i - 1))} is \tcode{true}.
 Invalidates only the iterators and references to the erased elements.
 
 \pnum
@@ -4802,11 +4816,14 @@
 
 \pnum
 \throws
-Nothing unless an exception is thrown by the equality comparison or the predicate.
+Nothing unless an exception is thrown by the predicate.
 
 \pnum
 \complexity
-If the range \range{first}{last} is not empty, exactly \tcode{(last - first) - 1} applications of the corresponding predicate, otherwise no applications of the predicate.
+If \tcode{empty()} is \tcode{false},
+exactly \tcode{distance(begin(), end()) - 1} applications of
+the corresponding predicate,
+otherwise no applications of the predicate.
 \end{itemdescr}
 
 \indexlibrarymember{merge}{forward_list}%
@@ -5296,6 +5313,10 @@
 arguments for a template parameter
 named \tcode{Predicate} or \tcode{BinaryPredicate}
 shall meet the corresponding requirements in \ref{algorithms.requirements}.
+The semantics of \tcode{i + n} and \tcode{i - n},
+where \tcode{i} is an iterator into the list and \tcode{n} is an integer,
+are the same as those of \tcode{next(i, n)} and \tcode{prev(i, n)},
+respectively.
 For \tcode{merge} and \tcode{sort},
 the definitions and requirements in \ref{alg.sorting} apply.
 
@@ -5474,13 +5495,20 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{binary_pred} be \tcode{equal_to<>\{\}} for the first overload.
+
+\pnum
+\expects
+\tcode{binary_pred} is an equivalence relation.
+
 \pnum
 \effects
 Erases all but the first element from every
-consecutive group of equal elements referred to by the iterator \tcode{i} in the range
-\range{first + 1}{last} for which \tcode{*i == *(i-1)} (for the version of
-\tcode{unique} with no arguments) or \tcode{binary_pred(*i, *(i - 1))} (for the version of
-\tcode{unique} with a predicate argument) holds.
+consecutive group of equivalent elements.
+That is, for a nonempty list, erases all elements referred to
+by the iterator \tcode{i} in the range \range{begin() + 1}{end()}
+for which \tcode{binary_pred(*i, *(i - 1))} is \tcode{true}.
 Invalidates only the iterators and references to the erased elements.
 
 \pnum
@@ -5489,18 +5517,12 @@
 
 \pnum
 \throws
-Nothing unless an exception is thrown by
-\tcode{*i == *(i-1)}
-or
-\tcode{pred(*i, *(i - 1))}.
+Nothing unless an exception is thrown by the predicate.
 
 \pnum
 \complexity
-If the range
-\tcode{[first, last)}
-is not empty, exactly
-\tcode{(last - first) - 1}
-applications of the corresponding predicate,
+If \tcode{empty()} is \tcode{false},
+exactly \tcode{size() - 1} applications of the corresponding predicate,
 otherwise no applications of the predicate.
 \end{itemdescr}
 
@@ -9695,6 +9717,12 @@
 exception is thrown by the swap of the adaptor's \tcode{Container} or
 \tcode{Compare} object (if any).
 
+\pnum
+A constructor template of a container adaptor
+shall not participate in overload resolution
+if it has an \tcode{InputIterator} template parameter and
+a type that does not qualify as an input iterator is deduced for that parameter.
+
 \pnum
 A deduction guide for a container adaptor shall not participate in overload resolution if any of the following are true:
 \begin{itemize}
@@ -9705,6 +9733,11 @@
 \item It has both \tcode{Container} and \tcode{Allocator} template parameters, and \tcode{uses_allocator_v<Container, Allocator>} is \tcode{false}.
 \end{itemize}
 
+\pnum
+The exposition-only alias template \exposid{iter-value-type}
+defined in \ref{sequences.general}
+may appear in deduction guides for container adaptors.
+
 \rSec2[queue.syn]{Header \tcode{<queue>} synopsis}
 
 \indexheader{queue}
@@ -10087,18 +10120,29 @@
     explicit priority_queue(const Compare& x) : priority_queue(x, Container()) {}
     priority_queue(const Compare& x, const Container&);
     priority_queue(const Compare& x, Container&&);
+    template<class InputIterator>
+      priority_queue(InputIterator first, InputIterator last, const Compare& x = Compare());
     template<class InputIterator>
       priority_queue(InputIterator first, InputIterator last, const Compare& x,
                      const Container&);
     template<class InputIterator>
-      priority_queue(InputIterator first, InputIterator last,
-                     const Compare& x = Compare(), Container&& = Container());
+      priority_queue(InputIterator first, InputIterator last, const Compare& x,
+                     Container&&);
     template<class Alloc> explicit priority_queue(const Alloc&);
     template<class Alloc> priority_queue(const Compare&, const Alloc&);
     template<class Alloc> priority_queue(const Compare&, const Container&, const Alloc&);
     template<class Alloc> priority_queue(const Compare&, Container&&, const Alloc&);
     template<class Alloc> priority_queue(const priority_queue&, const Alloc&);
     template<class Alloc> priority_queue(priority_queue&&, const Alloc&);
+    template<class InputIterator, class Alloc>
+      priority_queue(InputIterator, InputIterator, const Alloc&);
+    template<class InputIterator, class Alloc>
+      priority_queue(InputIterator, InputIterator, const Compare&, const Alloc&);
+    template<class InputIterator, class Alloc>
+      priority_queue(InputIterator, InputIterator, const Compare&, const Container&,
+                     const Alloc&);
+    template<class InputIterator, class Alloc>
+      priority_queue(InputIterator, InputIterator, const Compare&, Container&&, const Alloc&);
 
     [[nodiscard]] bool empty() const { return c.empty(); }
     size_type size()  const          { return c.size(); }
@@ -10117,15 +10161,30 @@
       -> priority_queue<typename Container::value_type, Container, Compare>;
 
   template<class InputIterator,
-           class Compare = less<typename iterator_traits<InputIterator>::value_type>,
-           class Container = vector<typename iterator_traits<InputIterator>::value_type>>
+           class Compare = less<@\exposid{iter-value-type}@<InputIterator>>,
+           class Container = vector<@\exposid{iter-value-type}@<InputIterator>>>
     priority_queue(InputIterator, InputIterator, Compare = Compare(), Container = Container())
-      -> priority_queue<typename iterator_traits<InputIterator>::value_type, Container, Compare>;
+      -> priority_queue<@\exposid{iter-value-type}@<InputIterator>, Container, Compare>;
 
   template<class Compare, class Container, class Allocator>
     priority_queue(Compare, Container, Allocator)
       -> priority_queue<typename Container::value_type, Container, Compare>;
 
+  template<class InputIterator, class Allocator>
+    priority_queue(InputIterator, InputIterator, Allocator)
+      -> priority_queue<@\exposid{iter-value-type}@<InputIterator>,
+                        vector<@\exposid{iter-value-type}@<InputIterator>, Allocator>,
+                        less<@\exposid{iter-value-type}@<InputIterator>>>;
+
+  template<class InputIterator, class Compare, class Allocator>
+    priority_queue(InputIterator, InputIterator, Compare, Allocator)
+      -> priority_queue<@\exposid{iter-value-type}@<InputIterator>,
+                        vector<@\exposid{iter-value-type}@<InputIterator>, Allocator>, Compare>;
+
+  template<class InputIterator, class Compare, class Container, class Allocator>
+    priority_queue(InputIterator, InputIterator, Compare, Container, Allocator)
+      -> priority_queue<typename Container::value_type, Container, Compare>;
+
   // no equality is provided
 
   template<class T, class Container, class Compare, class Alloc>
@@ -10158,13 +10217,32 @@
 \tcode{make_heap(c.begin(), c.end(), comp)}.
 \end{itemdescr}
 
+\indexlibraryctor{priority_queue}%
+\begin{itemdecl}
+template<class InputIterator>
+  priority_queue(InputIterator first, InputIterator last, const Compare& x = Compare());
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\expects
+\tcode{x} defines a strict weak ordering\iref{alg.sorting}.
+
+\pnum
+\effects
+Initializes \tcode{c} with
+\tcode{first} as the first argument and
+\tcode{last} as the second argument, and
+initializes \tcode{comp} with \tcode{x};
+then calls \tcode{make_heap(c.begin(), c.end(), comp)}.
+\end{itemdescr}
+
 \indexlibraryctor{priority_queue}%
 \begin{itemdecl}
 template<class InputIterator>
   priority_queue(InputIterator first, InputIterator last, const Compare& x, const Container& y);
 template<class InputIterator>
-  priority_queue(InputIterator first, InputIterator last, const Compare& x = Compare(),
-                 Container&& y = Container());
+  priority_queue(InputIterator first, InputIterator last, const Compare& x, Container&& y);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -10265,6 +10343,75 @@
 as the second argument, and initializes \tcode{comp} with \tcode{std::move(q.comp)}.
 \end{itemdescr}
 
+\indexlibraryctor{priority_queue}%
+\begin{itemdecl}
+template<class InputIterator, class Alloc>
+  priority_queue(InputIterator first, InputIterator last, const Alloc& a);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Initializes \tcode{c} with
+\tcode{first} as the first argument,
+\tcode{last} as the second argument, and
+\tcode{a} as the third argument, and
+value-initializes \tcode{comp};
+calls \tcode{make_heap(c.begin(), c.end(), comp)}.
+\end{itemdescr}
+
+\indexlibraryctor{priority_queue}%
+\begin{itemdecl}
+template<class InputIterator, class Alloc>
+  priority_queue(InputIterator first, InputIterator last, const Compare& compare, const Alloc& a);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Initializes \tcode{c} with
+\tcode{first} as the first argument,
+\tcode{last} as the second argument, and
+\tcode{a} as the third argument, and
+initializes \tcode{comp} with \tcode{compare};
+calls \tcode{make_heap(c.begin(), c.end(), comp)}.
+\end{itemdescr}
+
+\indexlibraryctor{priority_queue}%
+\begin{itemdecl}
+template<class InputIterator, class Alloc>
+  priority_queue(InputIterator first, InputIterator last, const Compare& compare,
+                 const Container& cont, const Alloc& a);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Initializes \tcode{c} with
+\tcode{cont} as the first argument and \tcode{a} as the second argument, and
+initializes \tcode{comp} with \tcode{compare};
+calls \tcode{c.insert(c.end(), first, last)}; and
+finally calls \tcode{make_heap(c.begin(), c.end(), comp)}.
+\end{itemdescr}
+
+\indexlibraryctor{priority_queue}%
+\begin{itemdecl}
+template<class InputIterator, class Alloc>
+  priority_queue(InputIterator first, InputIterator last, const Compare& compare, Container&& cont,
+                 const Alloc& a);
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Initializes \tcode{c} with
+\tcode{std::move(cont)} as the first argument and
+\tcode{a} as the second argument, and
+initializes \tcode{comp} with \tcode{compare};
+calls \tcode{c.insert(c.end(), first, last)}; and
+finally calls \tcode{make_heap(c.begin(), c.end(), comp)}.
+\end{itemdescr}
+
 \rSec3[priqueue.members]{Members}
 
 \indexlibrarymember{push}{priority_queue}%