[sequences] Add exposition-only alias template for deduction guides.

Author: jwakely

source/containers.tex

@@ -2928,6 +2928,14 @@
 \tcode{<list>}, and \tcode{<vector>} define class templates that meet the
 requirements for sequence containers.
 
+\pnum
+The following exposition-only alias template may appear in deduction guides for sequence containers:
+
+\begin{codeblock}
+template<class InputIterator>
+  using @\placeholdernc{iter-value-type}@ = typename iterator_traits<InputIterator>::value_type;  // \expos
+\end{codeblock}
+
 \rSec2[array.syn]{Header \tcode{<array>} synopsis}
 
 \indexhdr{array}%
@@ -3501,10 +3509,9 @@
     void     clear() noexcept;
   };
 
-  template<class InputIterator,
-           class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
+  template<class InputIterator, class Allocator = allocator<@\placeholder{iter-value-type}@<InputIterator>>>
     deque(InputIterator, InputIterator, Allocator = Allocator())
-      -> deque<typename iterator_traits<InputIterator>::value_type, Allocator>;
+      -> deque<@\placeholder{iter-value-type}@<InputIterator>, Allocator>;
 
   // \ref{deque.special}, specialized algorithms
   template<class T, class Allocator>
@@ -3890,10 +3897,9 @@
     void reverse() noexcept;
   };
 
-  template<class InputIterator,
-           class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
+  template<class InputIterator, class Allocator = allocator<@\placeholder{iter-value-type}@<InputIterator>>>
     forward_list(InputIterator, InputIterator, Allocator = Allocator())
-      -> forward_list<typename iterator_traits<InputIterator>::value_type, Allocator>;
+      -> forward_list<@\placeholder{iter-value-type}@<InputIterator>, Allocator>;
 
   // \ref{forwardlist.spec}, specialized algorithms
   template<class T, class Allocator>
@@ -4597,10 +4603,9 @@
     void reverse() noexcept;
   };
 
-  template<class InputIterator,
-           class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
+  template<class InputIterator, class Allocator = allocator<@\placeholder{iter-value-type}@<InputIterator>>>
     list(InputIterator, InputIterator, Allocator = Allocator())
-      -> list<typename iterator_traits<InputIterator>::value_type, Allocator>;
+      -> list<@\placeholder{iter-value-type}@<InputIterator>, Allocator>;
 
   // \ref{list.special}, specialized algorithms
   template<class T, class Allocator>
@@ -5259,10 +5264,9 @@
     void     clear() noexcept;
   };
 
-  template<class InputIterator,
-           class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
+  template<class InputIterator, class Allocator = allocator<@\placeholder{iter-value-type}@<InputIterator>>>
     vector(InputIterator, InputIterator, Allocator = Allocator())
-      -> vector<typename iterator_traits<InputIterator>::value_type, Allocator>;
+      -> vector<@\placeholder{iter-value-type}@<InputIterator>, Allocator>;
 
   // \ref{vector.special}, specialized algorithms
   template<class T, class Allocator>