Don't do this ever please. If you have to, please comment it.

wtf.cc

#include <stdio.h>

struct foo {
    struct dummy {
        int i;
    };
    typedef int dummy::*_bool;

    foo(int f) : f_(f) {}
    int f_;

    operator _bool() const {
        return f_ ? &dummy::i: 0;
    }
};

int main() {
    foo bar(3); 

    if (bar) {
        puts("yes");
    } else {
        puts("no");
    }
}