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743. rvalue swap for shared_ptr

Section: 20.3.2.2.9 [util.smartptr.shared.spec] Status: CD1 Submitter: Howard Hinnant Opened: 2007-10-10 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

When the LWG looked at 674(i) in Kona the following note was made:

We may need to open an issue to deal with the question of whether shared_ptr needs an rvalue swap.

This issue was opened in response to that note.

I believe allowing rvalue shared_ptrs to swap is both appropriate, and consistent with how other library components are currently specified.

[ Bellevue: ]

Concern that the three signatures for swap is needlessly complicated, but this issue merely brings shared_ptr into equal complexity with the rest of the library. Will open a new issue for concern about triplicate signatures.

Adopt issue as written.

Proposed resolution:

Change the synopsis in 20.3.2.2 [util.smartptr.shared]: 

void swap(shared_ptr&& r);
...
template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b);
template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b);
template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);

Change 20.3.2.2.5 [util.smartptr.shared.mod]: 

void swap(shared_ptr&& r);

Change 20.3.2.2.9 [util.smartptr.shared.spec]: 

template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b);
template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b);
template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);