* include/bits/forward_list.h (forward_list::assign): Dispatch to new

	functions based on assignability of elements.
	(forward_list::_M_assign): Add overloaded functions for assigning
	via assignment or via clearing and insertion.
	(forward_list::_M_assign_val): Likewise.
	(forward_list::_M_move_assign(forward_list&&, false_type)): Do not
	erase elements that are not moved.
	* include/bits/forward_list.tcc (forward_list::operator=): Call
	assign() to copy elements.
	* testsuite/23_containers/forward_list/cons/10.cc: New.
	* testsuite/23_containers/forward_list/cons/11.cc: New.
	* testsuite/23_containers/forward_list/cons/12.cc: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@193057 138bc75d-0d04-0410-961f-82ee72b054a4

2 files changed, 71 insertions, 35 deletions

diff --git a/libstdc++-v3/include/bits/forward_list.h b/libstdc++-v3/include/bits/forward_list.h
index 8d4915d0e4d..b40fe9b4a9f 100644
--- a/libstdc++-v3/include/bits/forward_list.h
+++ b/libstdc++-v3/include/bits/forward_list.h
@@ -589,7 +589,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  in the range [@a __first,@a __last).
        *
        *  Note that the assignment completely changes the %forward_list and
-       *  that the number of elements of the resulting %forward_list's is the
+       *  that the number of elements of the resulting %forward_list is the
        *  same as the number of elements assigned.  Old data is lost.
        */
       template<typename _InputIterator,
@@ -597,9 +597,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	void
         assign(_InputIterator __first, _InputIterator __last)
         {
-          clear();
-          insert_after(cbefore_begin(), __first, __last);
-        }
+	  typedef is_assignable<_Tp, decltype(*__first)> __assignable;
+	  _M_assign(__first, __last, __assignable());
+	}
 
       /**
        *  @brief  Assigns a given value to a %forward_list.
@@ -613,10 +613,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        */
       void
       assign(size_type __n, const _Tp& __val)
-      {
-        clear();
-        insert_after(cbefore_begin(), __n, __val);
-      }
+      { _M_assign_n(__n, __val, is_copy_assignable<_Tp>()); }
 
       /**
        *  @brief  Assigns an initializer_list to a %forward_list.
@@ -628,10 +625,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        */
       void
       assign(std::initializer_list<_Tp> __il)
-      {
-        clear();
-        insert_after(cbefore_begin(), __il);
-      }
+      { assign(__il.begin(), __il.end()); }
 
       /// Get a copy of the memory allocation object.
       allocator_type
@@ -1255,13 +1249,70 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
         if (__list._M_get_Node_allocator() == this->_M_get_Node_allocator())
           _M_move_assign(std::move(__list), std::true_type());
         else
-          {
-            // The rvalue's allocator cannot be moved, or is not equal,
-            // so we need to individually move each element.
-            this->assign(std::__make_move_if_noexcept_iterator(__list.begin()),
-                         std::__make_move_if_noexcept_iterator(__list.end()));
-            __list.clear();
-          }
+	  // The rvalue's allocator cannot be moved, or is not equal,
+	  // so we need to individually move each element.
+	  this->assign(std::__make_move_if_noexcept_iterator(__list.begin()),
+		       std::__make_move_if_noexcept_iterator(__list.end()));
+      }
+
+      // Called by assign(_InputIterator, _InputIterator) if _Tp is
+      // CopyAssignable.
+      template<typename _InputIterator>
+	void
+        _M_assign(_InputIterator __first, _InputIterator __last, true_type)
+	{
+	  auto __prev = before_begin();
+	  auto __curr = begin();
+	  auto __end = end();
+	  while (__curr != __end && __first != __last)
+	    {
+	      *__curr = *__first;
+	      ++__prev;
+	      ++__curr;
+	      ++__first;
+	    }
+	  if (__first != __last)
+	    insert_after(__prev, __first, __last);
+	  else if (__curr != __end)
+	    erase_after(__prev, __end);
+        }
+
+      // Called by assign(_InputIterator, _InputIterator) if _Tp is not
+      // CopyAssignable.
+      template<typename _InputIterator>
+	void
+        _M_assign(_InputIterator __first, _InputIterator __last, false_type)
+	{
+	  clear();
+	  insert_after(cbefore_begin(), __first, __last);
+	}
+
+      // Called by assign(size_type, const _Tp&) if Tp is CopyAssignable
+      void
+      _M_assign_n(size_type __n, const _Tp& __val, true_type)
+      {
+	auto __prev = before_begin();
+	auto __curr = begin();
+	auto __end = end();
+	while (__curr != __end && __n > 0)
+	  {
+	    *__curr = __val;
+	    ++__prev;
+	    ++__curr;
+	    --__n;
+	  }
+	if (__n > 0)
+	  insert_after(__prev, __n, __val);
+	else if (__curr != __end)
+	  erase_after(__prev, __end);
+      }
+
+      // Called by assign(size_type, const _Tp&) if Tp is non-CopyAssignable
+      void
+      _M_assign_n(size_type __n, const _Tp& __val, false_type)
+      {
+	clear();
+	insert_after(cbefore_begin(), __n, __val);
       }
     };
 
diff --git a/libstdc++-v3/include/bits/forward_list.tcc b/libstdc++-v3/include/bits/forward_list.tcc
index 4f9a7fad4eb..7395b2029ad 100644
--- a/libstdc++-v3/include/bits/forward_list.tcc
+++ b/libstdc++-v3/include/bits/forward_list.tcc
@@ -165,22 +165,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 		}
 	      std::__alloc_on_copy(__this_alloc, __that_alloc);
             }
-          iterator __prev1 = before_begin();
-          iterator __curr1 = begin();
-          iterator __last1 = end();
-          const_iterator __first2 = __list.cbegin();
-          const_iterator __last2 = __list.cend();
-          while (__curr1 != __last1 && __first2 != __last2)
-            {
-              *__curr1 = *__first2;
-              ++__prev1;
-              ++__curr1;
-              ++__first2;
-            }
-          if (__first2 == __last2)
-            erase_after(__prev1, __last1);
-          else
-            insert_after(__prev1, __first2, __last2);
+	  assign(__list.cbegin(), __list.cend());
         }
       return *this;
     }