This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++14 status.
std::allocator_traits<std::allocator<T>>::propagate_on_container_move_assignment
Section: 20.2.10 [default.allocator] Status: C++14 Submitter: Ai Azuma Opened: 2011-11-08 Last modified: 2016-01-28
Priority: Not Prioritized
View other active issues in [default.allocator].
View all other issues in [default.allocator].
View all issues with C++14 status.
Discussion:
"std::allocator_traits<std::allocator<T>>::propagate_on_container_move_assignment::value
"
is specified as "false", according to (20.2.10 [default.allocator]) and (20.2.9.2 [allocator.traits.types]).
However, according to (24.2.2 [container.requirements.general]), this specification leads to the unneeded requirements
(MoveInsertable
and MoveAssignable
of the value type) on the move assignment operator of containers
with the default allocator.
typedef std::true_type propagate_on_container_move_assignment;
"
in the definition of std::allocator
class template,
std::allocator_traits
" class template for "std::allocator
"
class template, in which "propagate_on_container_move_assignment
"
nested typedef is specified as "std::true_type
".
Pablo prefers the first resolution.
[2011-12-02: Pablo comments]
This issue has potentially some overlap with 2108(i). Should the trait always_compare_equal
been added, this issue's resolution should be improved based on that.
[2012, Kona]
Move to Ready.
[2012, Portland: applied to WP]
Proposed resolution:
This wording is relative to the FDIS.
Change 20.2.10 [default.allocator], the class template allocator
synopsis as indicated:
namespace std { template <class T> class allocator; // specialize forvoid
: template <> class allocator<void> { public: typedef void* pointer; typedef const void* const_pointer; // reference-to-void
members are impossible. typedef void value_type; template <class U> struct rebind { typedef allocator<U> other; }; }; template <class T> class allocator { public: typedef size_t size_type; typedef ptrdiff_t difference_type; typedef T* pointer; typedef const T* const_pointer; typedef T& reference; typedef const T& const_reference; typedef T value_type; template <class U> struct rebind { typedef allocator<U> other; }; typedef true_type propagate_on_container_move_assignment; […] }; }