LWG3875 std::ranges::repeat_view<T, IntegerClass>::iterator may be ill-formed

Author: burblebee

source/ranges.tex

@@ -214,8 +214,7 @@
 
   // \ref{range.repeat}, repeat view
   template<@\libconcept{move_constructible}@ T, @\libconcept{semiregular}@ Bound = unreachable_sentinel_t>
-    requires (is_object_v<T> && @\libconcept{same_as}@<T, remove_cv_t<T>>
-      && (@\exposid{is-integer-like}@<Bound> || @\libconcept{same_as}@<Bound, unreachable_sentinel_t>))
+    requires @\seebelow@
   class repeat_view;                                                                // freestanding
 
   namespace views { inline constexpr @\unspecnc@ repeat = @\unspecnc@; }            // freestanding
@@ -3400,9 +3399,14 @@
 
 \begin{codeblock}
 namespace std::ranges {
+  template<class T>
+    concept @\defexposconceptnc{integer-like-with-usable-difference-type}@ =  // \expos
+      @\exposid{is-signed-integer-like}@<T> || (@\exposid{is-integer-like}@<T> && @\libconcept{weakly_incrementable}@<T>);
+
   template<@\libconcept{move_constructible}@ T, @\libconcept{semiregular}@ Bound = unreachable_sentinel_t>
     requires (is_object_v<T> && @\libconcept{same_as}@<T, remove_cv_t<T>> &&
-              (@\exposid{is-integer-like}@<Bound> || @\libconcept{same_as}@<Bound, unreachable_sentinel_t>))
+              (@\exposconcept{integer-like-with-usable-difference-type}@<Bound> ||
+               @\libconcept{same_as}@<Bound, unreachable_sentinel_t>))
   class @\libglobal{repeat_view}@ : public view_interface<repeat_view<T, Bound>> {
   private:
     // \ref{range.repeat.iterator}, class \tcode{repeat_view::\exposid{iterator}}
@@ -3539,9 +3543,10 @@
 
 \begin{codeblock}
 namespace std::ranges {
-  template<@\libconcept{move_constructible}@ T, @\libconcept{semiregular}@ Bound = unreachable_sentinel_t>
+  template<@\libconcept{move_constructible}@ T, @\libconcept{semiregular}@ Bound>
     requires (is_object_v<T> && @\libconcept{same_as}@<T, remove_cv_t<T>> &&
-              (@\exposid{is-integer-like}@<Bound> || @\libconcept{same_as}@<Bound, unreachable_sentinel_t>))
+              (@\exposconcept{integer-like-with-usable-difference-type}@<Bound> ||
+               @\libconcept{same_as}@<Bound, unreachable_sentinel_t>))
   class repeat_view<T, Bound>::@\exposid{iterator}@ {
   private:
     using @\exposidnc{index-type}@ =                          // \expos
@@ -3555,9 +3560,7 @@
     using iterator_concept = random_access_iterator_tag;
     using iterator_category = random_access_iterator_tag;
     using value_type = T;
-    using difference_type = conditional_t<@\exposid{is-signed-integer-like}@<@\exposid{index-type}@>,
-        @\exposid{index-type}@,
-        @\placeholdernc{IOTA-DIFF-T}@(@\exposid{index-type}@)>;
+    using difference_type = @\seebelow@;
 
     @\exposid{iterator}@() = default;
 
@@ -3585,6 +3588,12 @@
 }
 \end{codeblock}
 
+\pnum
+If \tcode{\exposid{is-signed-integer-like}<\exposid{index-type}>} is \tcode{true},
+the member \grammarterm{typedef-name} \tcode{difference_type}
+denotes \exposid{index-type}.
+Otherwise, it denotes \tcode{\placeholdernc{IOTA-DIFF-T}(\exposid{index-type})}\iref{range.iota.view}.
+
 \indexlibraryctor{repeat_view::\exposid{iterator}}%
 \begin{itemdecl}
 constexpr explicit @\exposid{iterator}@(const T* value, @\exposid{index-type}@ b = @\exposid{index-type}@());