LWG2901 Variants cannot properly support allocators

Author: Dawn Perchik

source/utilities.tex

@@ -4189,10 +4189,6 @@
   template <class T> struct hash;
   template <class... Types> struct hash<variant<Types...>>;
   template <> struct hash<monostate>;
-
-  // \ref{variant.traits}, allocator-related traits
-  template <class T, class Alloc> struct uses_allocator;
-  template <class... Types, class Alloc> struct uses_allocator<variant<Types...>, Alloc>;
 }
 \end{codeblock}
 
@@ -4222,26 +4218,6 @@
       template <size_t I, class U, class... Args>
         constexpr explicit variant(in_place_index_t<I>, initializer_list<U>, Args&&...);
 
-      // allocator-extended constructors
-      template <class Alloc>
-        variant(allocator_arg_t, const Alloc&);
-      template <class Alloc>
-        variant(allocator_arg_t, const Alloc&, const variant&);
-      template <class Alloc>
-        variant(allocator_arg_t, const Alloc&, variant&&);
-      template <class Alloc, class T>
-        variant(allocator_arg_t, const Alloc&, T&&);
-      template <class Alloc, class T, class... Args>
-        variant(allocator_arg_t, const Alloc&, in_place_type_t<T>, Args&&...);
-      template <class Alloc, class T, class U, class... Args>
-        variant(allocator_arg_t, const Alloc&, in_place_type_t<T>,
-                initializer_list<U>, Args&&...);
-      template <class Alloc, size_t I, class... Args>
-        variant(allocator_arg_t, const Alloc&, in_place_index_t<I>, Args&&...);
-      template <class Alloc, size_t I, class U, class... Args>
-        variant(allocator_arg_t, const Alloc&, in_place_index_t<I>,
-                initializer_list<U>, Args&&...);
-
       // \ref{variant.dtor}, destructor
       ~variant();
 
@@ -4553,40 +4529,6 @@
 constructor shall be a constexpr constructor.
 \end{itemdescr}
 
-\indexlibrary{\idxcode{variant}!constructor}%
-\begin{itemdecl}
-// allocator-extended constructors
-template <class Alloc>
-  variant(allocator_arg_t, const Alloc& a);
-template <class Alloc>
-  variant(allocator_arg_t, const Alloc& a, const variant& v);
-template <class Alloc>
-  variant(allocator_arg_t, const Alloc& a, variant&& v);
-template <class Alloc, class T>
-  variant(allocator_arg_t, const Alloc& a, T&& t);
-template <class Alloc, class T, class... Args>
-  variant(allocator_arg_t, const Alloc& a, in_place_type_t<T>, Args&&... args);
-template <class Alloc, class T, class U, class... Args>
-  variant(allocator_arg_t, const Alloc& a, in_place_type_t<T>,
-          initializer_list<U> il, Args&&... args);
-template <class Alloc, size_t I, class... Args>
-  variant(allocator_arg_t, const Alloc& a, in_place_index_t<I>, Args&&... args);
-template <class Alloc, size_t I, class U, class... Args>
-  variant(allocator_arg_t, const Alloc& a, in_place_index_t<I>,
-          initializer_list<U> il, Args&&... args);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\requires
-\tcode{Alloc} shall meet the requirements for an Allocator~(\ref{allocator.requirements}).
-
-\pnum
-\effects
-Equivalent to the preceding constructors except that the contained value is
-constructed with uses-allocator construction~(\ref{allocator.uses.construction}).
-\end{itemdescr}
-
 \rSec3[variant.dtor]{Destructor}
 
 \indexlibrary{\idxcode{variant}!destructor}%
@@ -5423,27 +5365,6 @@
 \end{itemdescr}
 
 
-\rSec2[variant.traits]{Allocator-related traits}
-
-\indexlibrary{\idxcode{uses_allocator}!\idxcode{variant}}%
-\begin{itemdecl}
-template <class... Types, class Alloc>
-  struct uses_allocator<variant<Types...>, Alloc> : true_type { };
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\requires \tcode{Alloc} shall be an Allocator~(\ref{allocator.requirements}).
-
-\pnum
-\begin{note}
-Specialization of this trait informs other library components
-that variant can be constructed with an allocator,
-even though it does not have a nested \tcode{allocator_type}.
-\end{note}
-\end{itemdescr}
-
-
 \rSec1[any]{Storage for any type}
 
 \pnum

source/xrefdelta.tex

@@ -16,6 +16,7 @@
 
 % Removed features.
 %\removedxref{removed.label}
+\removedxref{variant.traits}
 
 % Renamed sections.
 %\movedxref{old.label}{new.label}