C++ 多态继承 求解释

#include <string.h>
#include<iostream>
using namespace std;

enum note{middleC,Csharp,Cflat};//删掉就不能通过


class instrument{
public:
    void play(note) const{
        cout<<"instrument::play"<<endl;
    }
};
class wind:public instrument{
    void play(note)const{
        cout<<"wind::play"<<endl;
    }
};
void tune(instrument& i){
    i.play(middleC);
}
int main()
{
    //wind flute;
    wind(flute); //这么定义为什么能通过？？？

    tune(flute);
    system("pause");
    return 0;
}