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#include <iostream>
using namespace std;
 
/**
* @brief Defines a passkey for type T.
*/
template <typename T>
class PassKey
{
private:
    // befriend T so that only T can create a PassKey object
    friend T;
 
    // make default constructor private so that only T can access it
    PassKey() {}
 
    // noncopyable, non-assignable so that key can not be re-used
    PassKey(const PassKey&) = delete;
    PassKey& operator=(const PassKey&) = delete;
};
 
struct B;
 
struct A
{
	void doSomething(PassKey<B>) const
	{}
};
 
struct B
{
	void callDoSomething(const A& a) const
	{
		a.doSomething({});
	}
};
 
 
 
int main() {
	A a;
	B b;
	b.callDoSomething(a);
	int FraudKey=0;
	a.doSomething(reinterpret_cast<PassKey<B>&>(FraudKey));
	return 0;
}

prog.cpp: In function ‘int main()’:
prog.cpp:45:55: error: use of deleted function ‘PassKey<T>::PassKey(const PassKey<T>&) [with T = B]’
  a.doSomething(reinterpret_cast<PassKey<B>&>(FraudKey));
                                                       ^
prog.cpp:18:5: note: declared here
     PassKey(const PassKey&) = delete;
     ^~~~~~~
prog.cpp:26:7: note:   initializing argument 1 of ‘void A::doSomething(PassKey<B>) const’
  void doSomething(PassKey<B>) const
       ^~~~~~~~~~~

Standard output is empty