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1278. Inconsistent return values for forward_list::insert_after

Section: 23.3.7.5 [forward.list.modifiers] Status: C++11 Submitter: Bo Persson Opened: 2009-11-25 Last modified: 2023-02-07

Priority: Not Prioritized

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Discussion:

After applying LDR149(i), forward_list now has 5 overloads of insert_after, all returning an iterator.

However, two of those - inserting a single object - return "An iterator pointing to a copy of x [the inserted object]" while the other three - inserting zero or more objects - return an iterator equivalent to the position parameter, pointing before any possibly inserted objects.

Is this the intended change?

I don't really know what insert_after(position, empty_range) should really return, but always returning position seems less than useful.

[ 2010-02-04 Howard adds: ]

I agree this inconsistency will be error prone and needs to be fixed. Additionally emplace_after's return value is unspecified.

[ 2010-02-04 Nico provides wording. ]

[ 2010 Pittsburgh: ]

We prefer to return an iterator to the last inserted element. Modify the proposed wording and then set to Ready.

[ 2010-03-15 Howard adds: ]

Wording updated and set to Ready.

Proposed resolution:

In forward_list modifiers [forwardlist.modifiers] make the following modifications: 

iterator insert_after(const_iterator position, size_type n, const T& x);

...

10 Returns: position. An iterator pointing to the last inserted copy of x or position if n == 0. 

template <class InputIterator>
  iterator insert_after(const_iterator position, InputIterator first, InputIterator last);

...

13 Returns: position. An iterator pointing to the last inserted element or position if first == last. 

iterator insert_after(const_iterator position, initializer_list<T> il);

...

15 Returns: position. An iterator pointing to the last inserted element or position if il is empty. 

template <class... Args>
  iterator emplace_after(const_iterator position, Args&&... args);

...

17 ...

Returns: An iterator pointing to the new constructed element from args.