当效率至关重要时map::operator[]与map.insert之间的选择

#include <iostream>
#include <map>
#include <iterator>
#include <algorithm>
using namespace std;
class Widget{
public:
Widget()
{

};
Widget(double weight);
Widget& operator=(double weight);
friend ostream& operator<<(ostream& os,Widget &w);
private:
double weight;
};

template<typename MapType,typename KeyArgType,typename ValueArgType>
typename MapType::iterator EfficentUpdateOrAdd(MapType& m,const KeyArgType& k,const ValueArgType& v)
{
typename MapType::iterator lb=m.lower_bound(k);
if(lb!=m.end()&&!(m.key_comp()(k,lb->first)))
{
lb->second=v;
return lb;
}
else
{
return m.insert(lb,typename MapType::value_type(k,v));
}
}
Widget::Widget(double weight)
{
this->weight=weight;
}
Widget& Widget::operator=(double weight)
{
Widget a;
a.weight=weight;
return a;
}
ostream& operator<<(ostream& os,Widget& w)
{
os<<w.weight;
return os;
}
int main()
{
map<int,Widget> m;
typedef map<int,Widget>::iterator IntWidgetMapItr;
IntWidgetMapItr it=EfficentUpdateOrAdd(m,1,1.0);
it=EfficentUpdateOrAdd(m,2,2.0);
it=EfficentUpdateOrAdd(m,3,3.0);
it=EfficentUpdateOrAdd(m,4,4.0);
it=EfficentUpdateOrAdd(m,5,5.0);
it=EfficentUpdateOrAdd(m,6,6.0);
it=EfficentUpdateOrAdd(m,7,7.0);
it=EfficentUpdateOrAdd(m,8,8.0);

for(pair<int,Widget> p:m)
{
cout<<p.second<<endl;//运算符重载
}
return 0;
}