C++复习swap and move

Swapping doubles is easily implemented with three copies, However, although the same logic works to swap larger types, it comes with a significant cost: Now the copies are very expensive. In C++11, if the right-hand side of the assignment operator(or constructor) is an rvalue, then if the object supports moving, we can automatically avoid copies.

function std::move exists that converts any lvalue(or rvalue)into an rvalue. Note that the name is misleading; std::move doesn't move anything; rather, it makes a value subject to be moved.

void swap(double &x,double &y){    double tmp=x;    x=y;    y=tmp;}//replace expensive copies with moves;void swap(vector<string> &x,vector<string> &y){    vector<string>tmp=static_cast<vector<string>&&>(x);    x=static_cast<vector<string>&&>(y);    y=static_cast<vector<string>&&>(tmp);}//The syntax of a static cast is daunting;void swap(vector<string>&x,vector<string>&y){    vector<string>tmp=std::move(x);    x=std::move(y);    y=std::move(tmp);}//move function.

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