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### 674. `shared_ptr` interface changes for consistency with N1856

Section: 20.3.2.2 [util.smartptr.shared] Status: CD1 Submitter: Peter Dimov Opened: 2007-05-05 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

N1856 does not propose any changes to `shared_ptr`. It needs to be updated to use a rvalue reference where appropriate and to interoperate with `unique_ptr` as it does with `auto_ptr`.

Proposed resolution:

Change 20.3.2.2 [util.smartptr.shared] as follows:

>     template<class Y> explicit shared_ptr(auto_ptr<Y>&&& r);
>     template<class Y, class D> explicit shared_ptr(const unique_ptr<Y,D>& r) = delete;
>     template<class Y, class D> explicit shared_ptr(unique_ptr<Y,D>&& r);
>     ...
>     template<class Y> shared_ptr& operator=(auto_ptr<Y>&&& r);
>     template<class Y, class D> shared_ptr& operator=(const unique_ptr<Y,D>& r) = delete;
>     template<class Y, class D> shared_ptr& operator=(unique_ptr<Y,D>&& r);

Change 20.3.2.2.2 [util.smartptr.shared.const] as follows:

>     template<class Y> shared_ptr(auto_ptr<Y>&&& r);

Add to 20.3.2.2.2 [util.smartptr.shared.const]:

>     template<class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);

> > Effects: Equivalent to `shared_ptr( r.release(), r.get_deleter() )` when `D` is not a reference type, `shared_ptr( r.release(), ref( r.get_deleter() ) )` otherwise.

> > Exception safety: If an exception is thrown, the constructor has no effect.

Change 20.3.2.2.4 [util.smartptr.shared.assign] as follows:

>     template<class Y> shared_ptr& operator=(auto_ptr<Y>&&& r);

Add to 20.3.2.2.4 [util.smartptr.shared.assign]:

>     template<class Y, class D> shared_ptr& operator=(unique_ptr<Y,D>&& r);

> > -4- Effects: Equivalent to `shared_ptr(std::move(r)).swap(*this)`.

> > -5- Returns: `*this`.

[ Kona (2007): We may need to open an issue (743) to deal with the question of whether `shared_ptr` needs an rvalue `swap`. ]