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### 770. std::function should use rvalue swap

Section: 20.14.17 [func.wrap] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-10 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

It is expected that typical implementations of `std::function` will use dynamic memory allocations at least under given conditions, so it seems appropriate to change the current lvalue swappabilty of this class to rvalue swappability.

Proposed resolution:

In 20.14 [function.objects], header `<functional>` synopsis, just below of

>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);

In 20.14.17.3 [func.wrap.func] class `function` definition, change

>     void swap(function&&);

In 20.14.17.3 [func.wrap.func], just below of

>     template <class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
>     template <class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
>     template <class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);

In 20.14.17.3.3 [func.wrap.func.mod] change

>     void swap(function&& other);

In 20.14.17.3.8 [func.wrap.func.alg] add the two overloads

>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&& f1, function<R(ArgTypes...)>& f2);
>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>&& f2);