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#include <iostream>
 
class Broken {
public:
    Broken(int i): read_only(read_write), read_write(i) {}
 
    int const& read_only;
 
    void set(int i) { read_write = i; }
 
private:
    int read_write;
};
 
int main() {
	Broken original(5);
	Broken copy(4);
	copy = original;
 
	std::cout << copy.read_only << "\n";
 
	original.set(42);
 
	std::cout << copy.read_only << "\n";
	return 0;
}

prog.cpp: In function 'int main()':
prog.cpp:18:7: error: use of deleted function 'Broken& Broken::operator=(const Broken&)'
  copy = original;
       ^
prog.cpp:3:7: note: 'Broken& Broken::operator=(const Broken&)' is implicitly deleted because the default definition would be ill-formed:
 class Broken {
       ^
prog.cpp:3:7: error: non-static reference member 'const int& Broken::read_only', can't use default assignment operator

Standard output is empty