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Using std::reference_wrapper as the key in a std::map

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再見小時候
再見小時候 2021-01-12 01:18

I have a bunch of objects in a class hierarchy and would like to make a std::map using references to those objects as the keys in the map. Its seems like

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  • 不要未来只要你来
    不要未来只要你来 (楼主)
    2021-01-12 02:03

    On Visual Studio 11 Beta, I get the same problem. Using the free version which calls the < operator solves the problem.

    #include
#include
using namespace::std;

class Object { 
    int _n1;
public:

    Object(int n = 0):_n1(n){};
    bool operator < (const Object& rhs) const {return this->_n1 < rhs._n1;} 
    friend ostream &operator << (ostream &stream, const Object& o) { stream << o._n1 << " "; return stream;}
};

struct ObjectLess{

    bool operator()(const Object& lhs, const Object& rhs) const 
    {
        return lhs, string> table;

    //Using the free function works
    std::map, string, ObjectLess> table;

    Object a(1);
    Object b(2);
    Object c(3);


    table[a]="One";
    table[c]="Three";
    table[b]="Two";

    for(auto y: table){
    cout << y.first << " " << y.second.c_str() << std::endl;
}


    return 0;
}

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