P2165R4 Compatibility between tuple and tuple-like objects

burblebee · tkoeppe · commit 45e1a7b4c482 · 2022-08-15T16:35:02.000+01:00
Editorial changes:
* Added cross references in [tuple.rel] pointing at
  [basic.lookup.argdep].
* Addedd cross reference in [pairs.pair] pointing at
  [range.utility.helpers] for "different-from".
* Reworded section title in [tuple.common.ref].
* Added references in synopsis.
diff --git a/source/containers.tex b/source/containers.tex
@@ -9308,14 +9308,14 @@
     typename iterator_traits<InputIterator>::value_type;                // \expos
 template<class InputIterator>
   using @\placeholder{iter-key-type}@ = remove_const_t<
-    typename iterator_traits<InputIterator>::value_type::first_type>;   // \expos
+    tuple_element_t<0, @\exposid{iter-value-type}@<InputIterator>>>;                // \expos
 template<class InputIterator>
   using @\placeholder{iter-mapped-type}@ =
-    typename iterator_traits<InputIterator>::value_type::second_type;   // \expos
+    tuple_element_t<1, @\exposid{iter-value-type}@<InputIterator>>;                 // \expos
 template<class InputIterator>
   using @\placeholder{iter-to-alloc-type}@ = pair<
-    add_const_t<typename iterator_traits<InputIterator>::value_type::first_type>,
-    typename iterator_traits<InputIterator>::value_type::second_type>;  // \expos
+    add_const_t<tuple_element_t<0, @\exposid{iter-value-type}@<InputIterator>>>,
+    tuple_element_t<1, @\exposid{iter-value-type}@<InputIterator>>>;                // \expos
 template<ranges::@\libconcept{input_range}@ Range>
   using @\exposid{range-key-type}@ =
     remove_const_t<typename ranges::range_value_t<Range>::first_type>;  // \expos
diff --git a/source/ranges.tex b/source/ranges.tex
@@ -1677,20 +1677,9 @@
       @\libconcept{convertible_to}@<From, To> &&
       !@\exposconcept{uses-nonqualification-pointer-conversion}@<decay_t<From>, decay_t<To>>;
 
-  template<class T>
-    concept @\defexposconceptnc{pair-like}@ =                                     // \expos
-      !is_reference_v<T> && requires(T t) {
-        typename tuple_size<T>::type;                       // ensures \tcode{tuple_size<T>} is complete
-        requires @\libconcept{derived_from}@<tuple_size<T>, integral_constant<size_t, 2>>;
-        typename tuple_element_t<0, remove_const_t<T>>;
-        typename tuple_element_t<1, remove_const_t<T>>;
-        { std::get<0>(t) } -> @\libconcept{convertible_to}@<const tuple_element_t<0, T>&>;
-        { std::get<1>(t) } -> @\libconcept{convertible_to}@<const tuple_element_t<1, T>&>;
-      };
-
   template<class T, class U, class V>
     concept @\defexposconceptnc{pair-like-convertible-from}@ =                    // \expos
-      !@\libconcept{range}@<T> && @\exposconcept{pair-like}@<T> &&
+      !@\libconcept{range}@<T> && !is_reference_v<T> && @\exposconcept{pair-like}@<T> &&
       @\libconcept{constructible_from}@<T, U, V> &&
       @\exposconcept{convertible-to-non-slicing}@<U, tuple_element_t<0, T>> &&
       @\libconcept{convertible_to}@<V, tuple_element_t<1, T>>;
@@ -7959,12 +7948,7 @@
 namespace std::ranges {
   template<class T, size_t N>
   concept @\defexposconcept{has-tuple-element}@ =                   // \expos
-    requires(T t) {
-      typename tuple_size<T>::type;
-      requires N < tuple_size_v<T>;
-      typename tuple_element_t<N, T>;
-      { std::get<N>(t) } -> @\libconcept{convertible_to}@<const tuple_element_t<N, T>&>;
-    };
+    @\exposconcept{tuple-like}@<T> && N < tuple_size_v<T>;
 
   template<class T, size_t N>
   concept @\defexposconcept{returnable-element}@ =                  // \expos
@@ -8594,9 +8578,6 @@
     (!(@\libconcept{bidirectional_range}@<Rs> && ...) && (@\libconcept{common_range}@<Rs> && ...)) ||
     ((@\libconcept{random_access_range}@<Rs> && ...) && (@\libconcept{sized_range}@<Rs> && ...));
 
-  template<class... Ts>
-    using @\exposid{tuple-or-pair}@ = @\seebelow@;                 // \expos
-
   template<class F, class Tuple>
   constexpr auto @\exposid{tuple-transform}@(F&& f, Tuple&& tuple) { // \expos
     return apply([&]<class... Ts>(Ts&&... elements) {
@@ -8664,17 +8645,6 @@
 }
 \end{codeblock}
 
-\pnum
-Given some pack of types \tcode{Ts},
-the alias template \exposid{tuple-or-pair} is defined as follows:
-\begin{itemize}
-\item
-If \tcode{sizeof...(Ts)} is 2,
-\tcode{\exposid{tuple-or-pair}<Ts...>} denotes \tcode{pair<Ts...>}.
-\item
-Otherwise, \tcode{\exposid{tuple-or-pair}<Ts...>} denotes \tcode{tuple<Ts...>}.
-\end{itemize}
-
 \pnum
 Two \tcode{zip_view} objects have the same underlying sequence if and only if
 the corresponding elements of \exposid{views_} are equal\iref{concepts.equality}
diff --git a/source/support.tex b/source/support.tex
@@ -718,6 +718,8 @@
 #define @\defnlibxname{cpp_lib_to_underlying}@                     202102L // also in \libheader{utility}
 #define @\defnlibxname{cpp_lib_transformation_trait_aliases}@      201304L // also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_transparent_operators}@             201510L // also in \libheader{memory}, \libheader{functional}
+#define @\defnlibxname{cpp_lib_tuple_like}@                        202207L
+  // also in \libheader{utility}, \libheader{tuple}, \libheader{map}, \libheader{unordered_map}
 #define @\defnlibxname{cpp_lib_tuple_element_t}@                   201402L // also in \libheader{tuple}
 #define @\defnlibxname{cpp_lib_tuples_by_type}@                    201304L // also in \libheader{utility}, \libheader{tuple}
 #define @\defnlibxname{cpp_lib_type_identity}@                     201806L // also in \libheader{type_traits}
diff --git a/source/utilities.tex b/source/utilities.tex
