Is this a parameter or a type?

Question

In a sample code (below) I am wondering what is the parameter passed to the getSocialSecurityNumber in the Citizen class. Why is it (Passkey<Government>) and not (Passkey<Government> x).

Is it related to class template / functor ?

#include <string>
#include <iostream>

using namespace std;


template <typename T>
class Passkey {
private:
    friend T;
    Passkey() {}
    Passkey(const Passkey&) {}
    Passkey& operator=(const Passkey&) = delete;
};

class Citizen {
public:
    string getSocialSecurityNumber(Passkey<Government>) const { return _socialSecurityNumber; };
                                   ^^^^ (here)

private:
    string _socialSecurityNumber;
};

class Government {
private:
    void printCitizenInfo(const Citizen &citizen) const;
};

void Government::printCitizenInfo(const Citizen &citizen) const {
    cout << "Citizen SSN: " << citizen.getSocialSecurityNumber(Passkey<Government>()) << endl;
}

Aha this is how "secure" code for government is written. – Slava Nov 06 '18 at 21:21 — Slava, Nov 06 '18 at 21:21
@Slava could you give me a little hint about it ? – Blood-HaZaRd Nov 06 '18 at 21:26 — Blood-HaZaRd, Nov 06 '18 at 21:26

score 3 · Accepted Answer · answered Nov 06 '18 at 21:20

3

Passkey<Government> is a type. The parameters is obviously not used, it has no name.

answered Nov 06 '18 at 21:20

Swordfish

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So what is the aim about it ? how is it used ? – Blood-HaZaRd Nov 06 '18 at 21:28
The parameter \*is not\* used. – Swordfish Nov 06 '18 at 21:31
Ok if I understood, it is only related to force the signature for invoking the function getSocialSecurityNumber – Blood-HaZaRd Nov 06 '18 at 21:32

Is this a parameter or a type?

1 Answers1