#include<bits/stdc++.h>
using namespace std;
struct int1{
  signed a;
  friend void operator =(int1 &m,signed g)
  {
  	m.a=g;
  }
};
signed main()
{
  int1 a1;
 } 

这段代码会编译错误，编译器里面显示“void operator=(int1&, int)' must be a nonstatic member function”，是怎么回事啊？