Effective C + + Notes _ clause 25 consider writing out a swap function that does not throw an exception

1 //swap in Lib2 namespaceSTD {3Template<typename t>4     voidSwap (t& A, t&b)5     {6 T Temp (a);7A =b;8b =temp;9     }Ten } One  A //Cons: You need to assign a lot of data, but sometimes you don't have to copy so much content - classWidgetimpl { -  Public: the     //... - Private: -     intA, B, C; -std::vector<Double> v;//There may be a lot of data to replicate for a long time +     //... - }; +  A classWidget { at  Public: -Widgets (Constwidget&RHS); -widget&operator= (Constwidget&RHS) -     { -         //... -*pimpl = *(Rhs.pimpl); in         //.... -     } to Private: +Widgetimpl *Pimpl; - }; the  * //for the above example, only the exchange of pointers is good, there is no need for all the value of the exchange.  $ //in order to solve this problem, the std::swap needs to be specific to the widget. White is specifically for widgetsPanax Notoginseng //design a swap function - //Solution Solutions the classWidget { +  Public: AWidgets (Constwidget&RHS); thewidget&operator= (Constwidget&RHS) +     { -         //... $*pimpl = *(Rhs.pimpl); $         //.... -     } -  the     //attention Yo, the point is up. achieve Real replacement work -     voidSwap (widget&Other )Wuyi     { the         usingStd::swap; - swap (Pimpl, other.pimpl); Wu     } -  About Private: $Widgetimpl *Pimpl; - }; -  - //Note that the following is a special swap for the Widget class that calls the widget's swap function A namespaceSTD { +Template<>//1. Full specificity the     voidSwap<widget> (widget& A, widget& b)//2. Indicates that this swap function is specific to the widget specialization -     { $ A.swap (b); the     } the } the  the //What about the face of class templates? -Template<typename t> in classWidgetimpl { the     //... the }; About  theTemplate<typename t> the classWidget { the     //... + }; -  the /*Bayi error Yo: C + + only allows the class templates to be biased, in function templates is not feasible the customers can fully templates the STD (template<>), but can not add new templates (or classes the or functions or anything else) into Std.  - */ - namespaceSTD { theTemplate<typename t> the     voidswap< widget<t> > (widget<t>& A, widget<t>&b) the     { the A.swap (b);  -     } the }; the  the //-----Solution-----94 namespaceWidgetstuff { the     classWidgetimpl { the      Public: the         //...98     Private: About         intA, B, C; -std::vector<Double> v;//There may be a lot of data to replicate for a long time101         //...102     };103 104     classWidget { the      Public:106Widgets (Constwidget&RHS);107widget&operator= (Constwidget&RHS)108         {109             //... the*pimpl = *(Rhs.pimpl);111             //.... the         }113  the         //attention Yo, the point is up. achieve Real replacement work the         voidSwap (widget&Other ) the         {117             usingStd::swap;118 swap (Pimpl, other.pimpl);119         } - 121     Private:122Widgetimpl *Pimpl;123     };124  theTemplate<typename t>126     voidSwap (widget<t>& A, widget<t>&b)127     { -A.swap (b);//calling the swap function in the widget129     } the}

Summarize:

When Std::swap is inefficient for your type, provide a swap member function and make sure that the function does not throw an exception.

If you provide a member swap, you should also provide a non-member swap to invoke the former. For classes (not templates), please also special std::swap.

You should use the using declaration for Std::swap when you call swap, and then call swap without any namespace qualification adornments.

It is good to have a "user defined type" for the Std template, but never try to add something new to Std.

Effective C + + Notes _ clause 25 consider writing out a swap function that does not throw an exception