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### 2123. `merge()` allocator requirements for lists versus forward lists

Section: 99 [forwardlist.ops] Status: C++14 Submitter: Nicolai Josuttis Opened: 2012-01-15 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

Sub-clause 24.3.10.5 [list.ops], p24 states for lists:

> The behavior is undefined if `this->get_allocator() != x.get_allocator()`.

But there is nothing like that for forward lists in 99 [forwardlist.ops], although I would expect the same undefined behavior there.

[2012, Kona]

Move to Ready.

[2012, Portland: applied to WP]

Proposed resolution:

This wording is relative to the FDIS.

1. Add a new paragraph after 99 [forwardlist.ops] p19 as indicated:

   >     void merge(forward_list<T,Allocator>& x);
   >     void merge(forward_list<T,Allocator>&& x);
   >     template <class Compare> void merge(forward_list<T,Allocator>& x, Compare comp);
   >     template <class Compare> void merge(forward_list<T,Allocator>&& x, Compare comp);

   > > […]

   > > -19- Effects: […]

   > > -?- Remarks: The behavior is undefined if `this->get_allocator() != x.get_allocator()`.