Revert the return type for `emplace_(back|front)` to `void` in C++14 and before

[mclow.lists]

Summary

In C++11/14, the return type of emplace_front and emplace_back was void. In http://wg21.link/p0084, Alan Talbot proposed changing the return type to return a reference to the newly created element.

We implemented that - but unilaterally.
This changes that, so that the change is only realized when building for C++17 or later.
This fixes https://llvm.org/bugs/show_bug.cgi?id=31680.

[EricWF]

I hate that we have to conditionalize this change at all, but your changes LGTM.

[hans]

This sounds like something we'll want to merge to the release branch when it lands?

[mclow.lists]

Landed as revision 292990.

[mclow.lists]

Landed as r292990.

include/deque

     void push_front(value_type&& v);
     void push_back(const value_type& v);
     void push_back(value_type&& v);
-    template <class... Args> reference emplace_front(Args&&... args);
-    template <class... Args> reference emplace_back(Args&&... args);
+    template <class... Args> reference emplace_front(Args&&... args);  // reference in C++17
+    template <class... Args> reference emplace_back(Args&&... args);   // reference in C++17
     template <class... Args> iterator emplace(const_iterator p, Args&&... args);
     iterator insert(const_iterator p, const value_type& v);
     iterator insert(const_iterator p, value_type&& v);

     void push_back(const value_type& __v);
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 #ifndef _LIBCPP_HAS_NO_VARIADICS
+#if _LIBCPP_STD_VER > 14
     template <class... _Args> reference emplace_front(_Args&&... __args);
-    template <class... _Args> reference emplace_back(_Args&&... __args);
+    template <class... _Args> reference emplace_back (_Args&&... __args);
+#else
+    template <class... _Args> void      emplace_front(_Args&&... __args);
+    template <class... _Args> void      emplace_back (_Args&&... __args);
+#endif
     template <class... _Args> iterator emplace(const_iterator __p, _Args&&... __args);
 #endif  // _LIBCPP_HAS_NO_VARIADICS
     void push_front(value_type&& __v);

 
 template <class _Tp, class _Allocator>
 template <class... _Args>
+#if _LIBCPP_STD_VER > 14
 typename deque<_Tp, _Allocator>::reference
+#else
+void
+#endif
 deque<_Tp, _Allocator>::emplace_back(_Args&&... __args)
 {
     allocator_type& __a = __base::__alloc();

     __alloc_traits::construct(__a, _VSTD::addressof(*__base::end()),
                               _VSTD::forward<_Args>(__args)...);
     ++__base::size();
+#if _LIBCPP_STD_VER > 14
     return *--__base::end();
+#endif
 }
 
 #endif  // _LIBCPP_HAS_NO_VARIADICS

 
 template <class _Tp, class _Allocator>
 template <class... _Args>
+#if _LIBCPP_STD_VER > 14
 typename deque<_Tp, _Allocator>::reference
+#else
+void
+#endif
 deque<_Tp, _Allocator>::emplace_front(_Args&&... __args)
 {
     allocator_type& __a = __base::__alloc();

     __alloc_traits::construct(__a, _VSTD::addressof(*--__base::begin()), _VSTD::forward<_Args>(__args)...);
     --__base::__start_;
     ++__base::size();
+#if _LIBCPP_STD_VER > 14
     return *__base::begin();
+#endif
 }
 
 #endif  // _LIBCPP_HAS_NO_VARIADICS

include/forward_list

     reference       front();
     const_reference front() const;
 
-    template <class... Args> reference emplace_front(Args&&... args);
+    template <class... Args> reference emplace_front(Args&&... args);  // reference in C++17
     void push_front(const value_type& v);
     void push_front(value_type&& v);
 

 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 #ifndef _LIBCPP_HAS_NO_VARIADICS
+#if _LIBCPP_STD_VER > 14
     template <class... _Args> reference emplace_front(_Args&&... __args);
+#else
+    template <class... _Args> void      emplace_front(_Args&&... __args);
 #endif
+#endif
     void push_front(value_type&& __v);
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
     void push_front(const value_type& __v);

 
 template <class _Tp, class _Alloc>
 template <class... _Args>
+#if _LIBCPP_STD_VER > 14
 typename forward_list<_Tp, _Alloc>::reference
+#else
+void
+#endif
 forward_list<_Tp, _Alloc>::emplace_front(_Args&&... __args)
 {
     __node_allocator& __a = base::__alloc();

                                   _VSTD::forward<_Args>(__args)...);
     __h->__next_ = base::__before_begin()->__next_;
     base::__before_begin()->__next_ = __h.release();
+#if _LIBCPP_STD_VER > 14
     return base::__before_begin()->__next_->__value_;
+#endif
 }
 
 #endif  // _LIBCPP_HAS_NO_VARIADICS

include/list

     size_type max_size() const noexcept;
 
     template <class... Args>
-        reference emplace_front(Args&&... args);
+        reference emplace_front(Args&&... args); // reference in C++17
     void pop_front();
     template <class... Args>
-        reference emplace_back(Args&&... args);
+        reference emplace_back(Args&&... args);  // reference in C++17
     void pop_back();
     void push_front(const value_type& x);
     void push_front(value_type&& x);

     void push_back(value_type&& __x);
 #ifndef _LIBCPP_HAS_NO_VARIADICS
     template <class... _Args>
+#if _LIBCPP_STD_VER > 14
        reference emplace_front(_Args&&... __args);
+#else
+       void      emplace_front(_Args&&... __args);
+#endif
     template <class... _Args>
+#if _LIBCPP_STD_VER > 14
         reference emplace_back(_Args&&... __args);
+#else
+       void       emplace_back(_Args&&... __args);
+#endif
     template <class... _Args>
         iterator emplace(const_iterator __p, _Args&&... __args);
 #endif  // _LIBCPP_HAS_NO_VARIADICS

 
 template <class _Tp, class _Alloc>
 template <class... _Args>
+#if _LIBCPP_STD_VER > 14
 typename list<_Tp, _Alloc>::reference
+#else
+void
+#endif
 list<_Tp, _Alloc>::emplace_front(_Args&&... __args)
 {
     __node_allocator& __na = base::__node_alloc();

     __node_alloc_traits::construct(__na, _VSTD::addressof(__hold->__value_), _VSTD::forward<_Args>(__args)...);
     __link_nodes_at_front(__hold.get()->__as_link(), __hold.get()->__as_link());
     ++base::__sz();
+#if _LIBCPP_STD_VER > 14
     return __hold.release()->__value_;
+#else
+    __hold.release();
+#endif
 }
 
 template <class _Tp, class _Alloc>
 template <class... _Args>
+#if _LIBCPP_STD_VER > 14
 typename list<_Tp, _Alloc>::reference
+#else
+void
+#endif
 list<_Tp, _Alloc>::emplace_back(_Args&&... __args)
 {
     __node_allocator& __na = base::__node_alloc();

     __link_pointer __nl = __hold->__as_link();
     __link_nodes_at_back(__nl, __nl);
     ++base::__sz();
+#if _LIBCPP_STD_VER > 14
     return __hold.release()->__value_;
+#else
+    __hold.release();
+#endif
 }
 
 template <class _Tp, class _Alloc>

include/queue

 
     void push(const value_type& v);
     void push(value_type&& v);
-    template <class... Args> reference emplace(Args&&... args);
+    template <class... Args> reference emplace(Args&&... args); // reference in C++17
     void pop();
 
     void swap(queue& q) noexcept(is_nothrow_swappable_v<Container>)

 #ifndef _LIBCPP_HAS_NO_VARIADICS
     template <class... _Args>
         _LIBCPP_INLINE_VISIBILITY
+#if _LIBCPP_STD_VER > 14
         reference emplace(_Args&&... __args)
             { return c.emplace_back(_VSTD::forward<_Args>(__args)...);}
+#else
+        void     emplace(_Args&&... __args)
+            {        c.emplace_back(_VSTD::forward<_Args>(__args)...);}
+#endif
 #endif  // _LIBCPP_HAS_NO_VARIADICS
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
     _LIBCPP_INLINE_VISIBILITY

include/stack

 
     void push(const value_type& x);
     void push(value_type&& x);
-    template <class... Args> reference emplace(Args&&... args);
+    template <class... Args> reference emplace(Args&&... args); // reference in C++17
     void pop();
 
     void swap(stack& c) noexcept(is_nothrow_swappable_v<Container>)

 #ifndef _LIBCPP_HAS_NO_VARIADICS
     template <class... _Args>
         _LIBCPP_INLINE_VISIBILITY
+#if _LIBCPP_STD_VER > 14
         reference emplace(_Args&&... __args)
         { return c.emplace_back(_VSTD::forward<_Args>(__args)...);}
+#else
+        void      emplace(_Args&&... __args)
+        {        c.emplace_back(_VSTD::forward<_Args>(__args)...);}
+#endif
 #endif  // _LIBCPP_HAS_NO_VARIADICS
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
     _LIBCPP_INLINE_VISIBILITY

include/vector

     void push_back(const value_type& x);
     void push_back(value_type&& x);
     template <class... Args>
-        reference emplace_back(Args&&... args);
+        reference emplace_back(Args&&... args); // reference in C++17
     void pop_back();
 
     template <class... Args> iterator emplace(const_iterator position, Args&&... args);

     const_reference back() const;
 
     void push_back(const value_type& x);
-    template <class... Args> reference emplace_back(Args&&... args);  // C++14
+    template <class... Args> reference emplace_back(Args&&... args);  // C++14; reference in C++17
     void pop_back();
 
     template <class... Args> iterator emplace(const_iterator position, Args&&... args);  // C++14

 #ifndef _LIBCPP_HAS_NO_VARIADICS
     template <class... _Args>
         _LIBCPP_INLINE_VISIBILITY
+#if _LIBCPP_STD_VER > 14
         reference emplace_back(_Args&&... __args);
+#else
+        void      emplace_back(_Args&&... __args);
+#endif
 #endif  // _LIBCPP_HAS_NO_VARIADICS
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
     _LIBCPP_INLINE_VISIBILITY

 template <class _Tp, class _Allocator>
 template <class... _Args>
 inline
+#if _LIBCPP_STD_VER > 14
 typename vector<_Tp, _Allocator>::reference
+#else
+void
+#endif
 vector<_Tp, _Allocator>::emplace_back(_Args&&... __args)
 {
     if (this->__end_ < this->__end_cap())

     }
     else
         __emplace_back_slow_path(_VSTD::forward<_Args>(__args)...);
+#if _LIBCPP_STD_VER > 14
     return this->back();
+#endif
 }
 
 #endif  // _LIBCPP_HAS_NO_VARIADICS

     void push_back(const value_type& __x);
 #if _LIBCPP_STD_VER > 11
     template <class... _Args>
-    _LIBCPP_INLINE_VISIBILITY reference emplace_back(_Args&&... __args) {
+#if _LIBCPP_STD_VER > 14
+    _LIBCPP_INLINE_VISIBILITY reference emplace_back(_Args&&... __args)
+#else
+    _LIBCPP_INLINE_VISIBILITY void      emplace_back(_Args&&... __args)
+#endif
+    {
         push_back ( value_type ( _VSTD::forward<_Args>(__args)... ));
+#if _LIBCPP_STD_VER > 14
         return this->back();
+#endif
     }
 #endif
 

test/std/containers/container.adaptors/queue/queue.defn/emplace.pass.cpp

 // <queue>
 
 // template <class... Args> reference emplace(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
+
 #include <queue>
 #include <cassert>
 
+#include "test_macros.h"
+
 #include "../../../Emplaceable.h"
 
 int main()

 {
     typedef Emplaceable T;
     std::queue<Emplaceable> q;
+#if TEST_STD_VER > 14
     T& r1 = q.emplace(1, 2.5);
     assert(&r1 == &q.back());
     T& r2 = q.emplace(2, 3.5);

     assert(&r2 == &q.back());
     T& r3 = q.emplace(3, 4.5);
     assert(&r3 == &q.back());
+    assert(&r1 == &q.front());
+#else
+    q.emplace(1, 2.5);
+    q.emplace(2, 3.5);
+    q.emplace(3, 4.5);
+#endif
+
     assert(q.size() == 3);
     assert(q.front() == Emplaceable(1, 2.5));
     assert(q.back() == Emplaceable(3, 4.5));
-    assert(&r3 == &q.back());
-    assert(&r1 == &q.front());
 }

test/std/containers/container.adaptors/stack/stack.defn/emplace.pass.cpp

 // <stack>
 
 // template <class... Args> reference emplace(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <stack>
 #include <cassert>
 
+#include "test_macros.h"
+
 #include "../../../Emplaceable.h"
 
 int main()

 {
     typedef Emplaceable T;
     std::stack<Emplaceable> q;
+#if TEST_STD_VER > 14
     T& r1 = q.emplace(1, 2.5);
     assert(&r1 == &q.top());
     T& r2 = q.emplace(2, 3.5);

     assert(&r2 == &q.top());
     T& r3 = q.emplace(3, 4.5);
     assert(&r3 == &q.top());
+#else
+    q.emplace(1, 2.5);
+    q.emplace(2, 3.5);
+    q.emplace(3, 4.5);
+#endif
     assert(q.size() == 3);
     assert(q.top() == Emplaceable(3, 4.5));
 }

test/std/containers/sequences/deque/deque.modifiers/emplace_back.pass.cpp

 // <deque>
 
 // template <class... Args> reference emplace_back(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <deque>
 #include <cstddef>

 test(C& c1)
 {
     typedef typename C::iterator I;
+    std::size_t c1_osize = c1.size();
+#if TEST_STD_VER > 14
     typedef typename C::reference Ref;
-    std::size_t c1_osize = c1.size();
     Ref ref = c1.emplace_back(Emplaceable(1, 2.5));
+#else
+              c1.emplace_back(Emplaceable(1, 2.5));
+#endif
     assert(c1.size() == c1_osize + 1);
     assert(distance(c1.begin(), c1.end())
                == static_cast<std::ptrdiff_t>(c1.size()));
     I i = c1.end();
     assert(*--i == Emplaceable(1, 2.5));
+#if TEST_STD_VER > 14
     assert(&(*i) == &ref);
+#endif
 }
 
 template <class C>

test/std/containers/sequences/deque/deque.modifiers/emplace_front.pass.cpp

 // <deque>
 
 // template <class... Args> reference emplace_front(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <deque>
 #include <cstddef>

 #include "test_macros.h"
 #include "../../../Emplaceable.h"
 #include "min_allocator.h"
+#include "test_allocator.h"
 
 template <class C>
 C

 test(C& c1)
 {
     typedef typename C::iterator I;
+    std::size_t c1_osize = c1.size();
+#if TEST_STD_VER > 14
     typedef typename C::reference Ref;
-    std::size_t c1_osize = c1.size();
     Ref res_ref = c1.emplace_front(Emplaceable(1, 2.5));
+#else
+                  c1.emplace_front(Emplaceable(1, 2.5));
+#endif
     assert(c1.size() == c1_osize + 1);
     assert(distance(c1.begin(), c1.end())
                == static_cast<std::ptrdiff_t>(c1.size()));
     I i = c1.begin();
     assert(*i == Emplaceable(1, 2.5));
+#if TEST_STD_VER > 14
     assert(&res_ref == &(*i));
+#endif
 }
 
 template <class C>

         for (int j = 0; j < N; ++j)
             testN<std::deque<Emplaceable, min_allocator<Emplaceable>> >(rng[i], rng[j]);
     }
+    {
+        std::deque<Tag_X, TaggingAllocator<Tag_X>> c;
+        c.emplace_front();
+        assert(c.size() == 1);
+        c.emplace_front(1, 2, 3);
+        assert(c.size() == 2);
+        c.emplace_front();
+        assert(c.size() == 3);
+        c.emplace_front(1, 2, 3);
+        assert(c.size() == 4);
+    }
 }

test/std/containers/sequences/forwardlist/forwardlist.modifiers/emplace_front.pass.cpp

 // <forward_list>
 
 // template <class... Args> reference emplace_front(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <forward_list>
 #include <cassert>
 
+#include "test_macros.h"
+
 #include "../../../Emplaceable.h"
 #include "min_allocator.h"
 

         typedef Emplaceable T;
         typedef std::forward_list<T> C;
         C c;
+#if TEST_STD_VER > 14
         T& r1 = c.emplace_front();
         assert(c.front() == Emplaceable());
         assert(&r1 == &c.front());

         T& r2 = c.emplace_front(1, 2.5);
         assert(c.front() == Emplaceable(1, 2.5));
         assert(&r2 == &c.front());
+#else
+        c.emplace_front();
+        assert(c.front() == Emplaceable());
+        assert(distance(c.begin(), c.end()) == 1);
+        c.emplace_front(1, 2.5);
+        assert(c.front() == Emplaceable(1, 2.5));
+#endif
         assert(*next(c.begin()) == Emplaceable());
         assert(distance(c.begin(), c.end()) == 2);
     }

         typedef Emplaceable T;
         typedef std::forward_list<T, min_allocator<T>> C;
         C c;
+#if TEST_STD_VER > 14
         T& r1 = c.emplace_front();
         assert(c.front() == Emplaceable());
         assert(&r1 == &c.front());

         T& r2 = c.emplace_front(1, 2.5);
         assert(c.front() == Emplaceable(1, 2.5));
         assert(&r2 == &c.front());
+#else
+        c.emplace_front();
+        assert(c.front() == Emplaceable());
+        assert(distance(c.begin(), c.end()) == 1);
+        c.emplace_front(1, 2.5);
+        assert(c.front() == Emplaceable(1, 2.5));
+#endif
         assert(*next(c.begin()) == Emplaceable());
         assert(distance(c.begin(), c.end()) == 2);
     }

test/std/containers/sequences/list/list.modifiers/emplace_back.pass.cpp

 // <list>
 
 // template <class... Args> reference emplace_back(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <list>
 #include <cassert>
 
+#include "test_macros.h"
 #include "min_allocator.h"
 
 class A

 {
     {
     std::list<A> c;
+#if TEST_STD_VER > 14
     A& r1 = c.emplace_back(2, 3.5);
     assert(c.size() == 1);
     assert(&r1 == &c.back());

     A& r2 = c.emplace_back(3, 4.5);
     assert(c.size() == 2);
     assert(&r2 == &c.back());
+#else
+    c.emplace_back(2, 3.5);
+    assert(c.size() == 1);
     assert(c.front().geti() == 2);
     assert(c.front().getd() == 3.5);
+    c.emplace_back(3, 4.5);
+    assert(c.size() == 2);
+#endif
+    assert(c.front().geti() == 2);
+    assert(c.front().getd() == 3.5);
     assert(c.back().geti() == 3);
     assert(c.back().getd() == 4.5);
     }
     {
     std::list<A, min_allocator<A>> c;
+#if TEST_STD_VER > 14
     A& r1 = c.emplace_back(2, 3.5);
     assert(c.size() == 1);
     assert(&r1 == &c.back());

     A& r2 = c.emplace_back(3, 4.5);
     assert(c.size() == 2);
     assert(&r2 == &c.back());
+#else
+    c.emplace_back(2, 3.5);
+    assert(c.size() == 1);
     assert(c.front().geti() == 2);
     assert(c.front().getd() == 3.5);
+    c.emplace_back(3, 4.5);
+    assert(c.size() == 2);
+#endif
+    assert(c.front().geti() == 2);
+    assert(c.front().getd() == 3.5);
     assert(c.back().geti() == 3);
     assert(c.back().getd() == 4.5);
     }

test/std/containers/sequences/list/list.modifiers/emplace_front.pass.cpp

 // <list>
 
 // template <class... Args> reference emplace_front(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <list>
 #include <cassert>

 {
     {
     std::list<A> c;
+#if TEST_STD_VER > 14
     A& r1 = c.emplace_front(2, 3.5);
     assert(c.size() == 1);
     assert(&r1 == &c.front());

     A& r2 = c.emplace_front(3, 4.5);
     assert(c.size() == 2);
     assert(&r2 == &c.front());
+#else
+    c.emplace_front(2, 3.5);
+    assert(c.size() == 1);
+    assert(c.front().geti() == 2);
+    assert(c.front().getd() == 3.5);
+    c.emplace_front(3, 4.5);
+    assert(c.size() == 2);
+#endif
     assert(c.front().geti() == 3);
     assert(c.front().getd() == 4.5);
     assert(c.back().geti() == 2);
     assert(c.back().getd() == 3.5);
     }
+
     {
     std::list<A, min_allocator<A>> c;
+#if TEST_STD_VER > 14
     A& r1 = c.emplace_front(2, 3.5);
     assert(c.size() == 1);
     assert(&r1 == &c.front());

     A& r2 = c.emplace_front(3, 4.5);
     assert(c.size() == 2);
     assert(&r2 == &c.front());
+#else
+    c.emplace_front(2, 3.5);
+    assert(c.size() == 1);
+    assert(c.front().geti() == 2);
+    assert(c.front().getd() == 3.5);
+    c.emplace_front(3, 4.5);
+    assert(c.size() == 2);
+#endif
     assert(c.front().geti() == 3);
     assert(c.front().getd() == 4.5);
     assert(c.back().geti() == 2);

test/std/containers/sequences/vector.bool/emplace_back.pass.cpp

 //  vector.bool
 
 // template <class... Args> reference emplace_back(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <vector>
 #include <cassert>
+#include "test_macros.h"
 #include "min_allocator.h"
 
 int main()

 {
     {
         typedef std::vector<bool> C;
+        C c;
+#if TEST_STD_VER > 14
         typedef C::reference Ref;
-        C c;
         Ref r1 = c.emplace_back();
         assert(c.size() == 1);
         assert(c.front() == false);

         r2 = false;
         assert(c.back() == false);
         r2 = true;
-        Ref r3 = c.emplace_back(1 == 1);
+#else
+        c.emplace_back();
+        assert(c.size() == 1);
+        assert(c.front() == false);
+        c.emplace_back(true);
+        assert(c.size() == 2);
+        assert(c.front() == false);
+        assert(c.back() == true);
+#endif
+        c.emplace_back(1 == 1);
         assert(c.size() == 3);
         assert(c.front() == false);
         assert(c[1] == true);
         assert(c.back() == true);
-        r3 = false;
-        assert(c.back() == false);
     }
     {
         typedef std::vector<bool, min_allocator<bool>> C;
-        typedef C::reference Ref;
         C c;
 
+#if TEST_STD_VER > 14
+        typedef C::reference Ref;
         Ref r1 = c.emplace_back();
         assert(c.size() == 1);
         assert(c.front() == false);

         r2 = false;
         assert(c.back() == false);
         r2 = true;
+#else
+        c.emplace_back();
+        assert(c.size() == 1);
+        assert(c.front() == false);
+        c.emplace_back(true);
+        assert(c.size() == 2);
+        assert(c.front() == false);
+        assert(c.back() == true);
+#endif
         c.emplace_back(1 == 1);
         assert(c.size() == 3);
         assert(c.front() == false);

test/std/containers/sequences/vector/vector.modifiers/emplace_back.pass.cpp

 // <vector>
 
 // template <class... Args> reference emplace_back(Args&&... args);
+// return type is 'reference' in C++17; 'void' before
 
 #include <vector>
 #include <cassert>
+#include "test_macros.h"
 #include "test_allocator.h"
 #include "min_allocator.h"
 #include "test_allocator.h"

 {
     {
         std::vector<A> c;
+#if TEST_STD_VER > 14
         A& r1 = c.emplace_back(2, 3.5);
         assert(c.size() == 1);
         assert(&r1 == &c.back());

         A& r2 = c.emplace_back(3, 4.5);
         assert(c.size() == 2);
         assert(&r2 == &c.back());
+#else
+        c.emplace_back(2, 3.5);
+        assert(c.size() == 1);
         assert(c.front().geti() == 2);
         assert(c.front().getd() == 3.5);
+        assert(is_contiguous_container_asan_correct(c));
+        c.emplace_back(3, 4.5);
+        assert(c.size() == 2);
+#endif
+        assert(c.front().geti() == 2);
+        assert(c.front().getd() == 3.5);
         assert(c.back().geti() == 3);
         assert(c.back().getd() == 4.5);
         assert(is_contiguous_container_asan_correct(c));

     }
     {
         std::vector<A, limited_allocator<A, 4> > c;
+#if TEST_STD_VER > 14
         A& r1 = c.emplace_back(2, 3.5);
         assert(c.size() == 1);
         assert(&r1 == &c.back());

         A& r2 = c.emplace_back(3, 4.5);
         assert(c.size() == 2);
         assert(&r2 == &c.back());
+#else
+        c.emplace_back(2, 3.5);
+        assert(c.size() == 1);
         assert(c.front().geti() == 2);
         assert(c.front().getd() == 3.5);
+        assert(is_contiguous_container_asan_correct(c));
+        c.emplace_back(3, 4.5);
+        assert(c.size() == 2);
+#endif
+        assert(c.front().geti() == 2);
+        assert(c.front().getd() == 3.5);
         assert(c.back().geti() == 3);
         assert(c.back().getd() == 4.5);
         assert(is_contiguous_container_asan_correct(c));

     }
     {
         std::vector<A, min_allocator<A>> c;
+#if TEST_STD_VER > 14
         A& r1 = c.emplace_back(2, 3.5);
         assert(c.size() == 1);
         assert(&r1 == &c.back());

         A& r2 = c.emplace_back(3, 4.5);
         assert(c.size() == 2);
         assert(&r2 == &c.back());
+#else
+        c.emplace_back(2, 3.5);
+        assert(c.size() == 1);
         assert(c.front().geti() == 2);
         assert(c.front().getd() == 3.5);
+        assert(is_contiguous_container_asan_correct(c));
+        c.emplace_back(3, 4.5);
+        assert(c.size() == 2);
+#endif
+        assert(c.front().geti() == 2);
+        assert(c.front().getd() == 3.5);
         assert(c.back().geti() == 3);
         assert(c.back().getd() == 4.5);
         assert(is_contiguous_container_asan_correct(c));