Merge 2022-07 LWG Motion 21

P2408R5 Ranges iterators as inputs to non-Ranges algorithms

Author: tkoeppe

source/algorithms.tex

@@ -69,6 +69,11 @@
 Throughout this Clause, where the template parameters are not constrained,
 the names of template parameters are used to express type requirements.
 \begin{itemize}
+\item
+  If an algorithm's \Fundescx{Effects} element specifies
+  that a value pointed to by any iterator passed as an argument is modified,
+  then the type of that argument shall meet
+  the requirements of a mutable iterator\iref{iterator.requirements}.
 \item
   If an algorithm's template parameter is named
   \tcode{InputIterator},
@@ -86,16 +91,18 @@
 \item
   If an algorithm's template parameter is named
   \tcode{ForwardIterator},
-  \tcode{ForwardIterator1}, or
-  \tcode{Forward\-Iterator2},
+  \tcode{ForwardIterator1},
+  \tcode{ForwardItera\-tor2}, or
+  \tcode{NoThrowForwardIterator},
   the template argument shall meet the
-  \oldconcept{ForwardIterator} requirements\iref{forward.iterators}.
+  \oldconcept{ForwardIterator} requirements\iref{forward.iterators}
+  if it is required to be a mutable iterator, or
+  model \libconcept{forward_iterator}\iref{iterator.concept.forward} otherwise.
 \item
   If an algorithm's template parameter is named
   \tcode{NoThrowForwardIterator},
-  the template argument shall meet the
-  \oldconcept{ForwardIterator} requirements\iref{forward.iterators}, and
-  is required to have the property that no exceptions are thrown
+  the template argument
+  is also required to have the property that no exceptions are thrown
   from increment, assignment, or comparison of, or
   indirection through, valid iterators.
 \item
@@ -104,28 +111,23 @@
   \tcode{Bidirectional\-Iterator1}, or
   \tcode{BidirectionalIterator2},
   the template argument shall meet the
-  \oldconcept{BidirectionalIterator} requirements\iref{bidirectional.iterators}.
+  \oldconcept{BidirectionalIterator} requirements\iref{bidirectional.iterators}
+  if it is required to be a mutable iterator, or model
+  \libconcept{bidirectional_iterator}\iref{iterator.concept.bidir} otherwise.
 \item
   If an algorithm's template parameter is named
   \tcode{RandomAccessIterator},
   \tcode{Random\-AccessIterator1}, or
   \tcode{RandomAccessIterator2},
   the template argument shall meet the
-  \oldconcept{RandomAccessIterator} requirements\iref{random.access.iterators}.
+  \oldconcept{RandomAccessIterator} requirements\iref{random.access.iterators}
+  if it is required to be a mutable iterator, or model
+  \libconcept{random_access_iterator}\iref{iterator.concept.random.access} otherwise.
 \end{itemize}
-
-\pnum
-If an algorithm's \effects element specifies
-that a value pointed to by any iterator passed as an argument is modified,
-then that algorithm has an additional type requirement:
-The type of that argument shall meet
-the requirements of a mutable iterator\iref{iterator.requirements}.
 \begin{note}
-This requirement does not affect arguments that are named
-\tcode{OutputIterator}, \tcode{OutputIterator1}, or \tcode{OutputIterator2},
-because output iterators must always be mutable, nor
-does it affect arguments that are constrained,
-for which mutability requirements are expressed explicitly.
+These requirements do not affect iterator arguments that are constrained,
+for which iterator category and mutability requirements
+are expressed explicitly.
 \end{note}
 
 \pnum
@@ -6033,8 +6035,8 @@
   \item
     For the overloads with no \tcode{ExecutionPolicy},
     let \tcode{T} be the value type of \tcode{InputIterator}.
-    If \tcode{InputIterator} meets
-    the \oldconcept{ForwardIterator} requirements,
+    If \tcode{InputIterator} models
+    \libconcept{forward_iterator}\iref{iterator.concept.forward},
     then there are no additional requirements for \tcode{T}.
     Otherwise, if \tcode{OutputIterator} meets
     the \oldconcept{ForwardIterator} requirements and
@@ -6339,8 +6341,8 @@
 \item
   \tcode{SampleIterator} meets
   the \oldconcept{RandomAccessIterator} requirements\iref{random.access.iterators}
-  unless \tcode{Pop\-ulat\-ion\-Iter\-ator} meets
-  the \oldconcept{ForwardIterator} requirements\iref{forward.iterators}.
+  unless \tcode{Pop\-ulat\-ion\-Iter\-ator}
+  models \libconcept{forward_iterator}\iref{iterator.concept.forward}.
 \item
   \tcode{remove_reference_t<UniformRandomBitGenerator>} meets
   the requirements of a uniform random bit generator type\iref{rand.req.urng}.
@@ -6369,8 +6371,8 @@
 \begin{itemize}
 \item
   For the overload in namespace \tcode{std},
-  stable if and only if \tcode{PopulationIterator} meets
-  the \oldconcept{For\-wardIterator} requirements.
+  stable if and only if \tcode{PopulationIterator}
+  models \libconcept{forward_iterator}.
   For the first overload in namespace \tcode{ranges},
   stable if and only if \tcode{I} models \libconcept{forward_iterator}.
 \item

source/regex.tex

@@ -2691,8 +2691,8 @@
 \begin{itemdescr}
 \pnum
 \expects
-\tcode{BidirectionalIterator} meets the
-\oldconcept{BidirectionalIterator} requirements\iref{bidirectional.iterators}.
+\tcode{BidirectionalIterator} models
+\libconcept{bidirectional_iterator}\iref{iterator.concept.bidir}.
 
 \pnum
 \effects
@@ -2881,8 +2881,8 @@
 \begin{itemdescr}
 \pnum
 \expects
-\tcode{BidirectionalIterator} meets the
-\oldconcept{BidirectionalIterator} requirements\iref{bidirectional.iterators}.
+\tcode{BidirectionalIterator} models
+\libconcept{bidirectional_iterator}\iref{iterator.concept.bidir}.
 
 \pnum
 \effects

source/support.tex

@@ -553,6 +553,8 @@
 \begin{codeblock}
 // all freestanding
 #define @\defnlibxname{cpp_lib_addressof_constexpr}@               201603L // also in \libheader{memory}
+#define @\defnlibxname{cpp_lib_algorithm_iterator_requirements}@   202207L
+  // also in \libheader{algorithm}, \libheader{numeric}, \libheader{memory}
 #define @\defnlibxname{cpp_lib_allocate_at_least}@                 202106L // also in \libheader{memory}
 #define @\defnlibxname{cpp_lib_allocator_traits_is_always_equal}@  201411L
   // also in \libheader{memory}, \libheader{scoped_allocator}, \libheader{string}, \libheader{deque}, \libheader{forward_list}, \libheader{list}, \libheader{vector},