gistfile1.cpp

#include <iostream>
#include <vector>

class Instance {
    const Instance* ref;
    int             value;
public:
    Instance (const Instance* other, int value) : 
         ref(ref), value(value) { }
};

class InstanceMgr {
    std::vector<Instance> repos;
public:
    InstanceMgr& add(int v) { 
        repos.emplace_back(repos.empty() ? nullptr : &repos.back(), v);
        return *this;
    }
};

int main(int argc, char* argv[]) {
    InstanceMgr mgr;
    mgr.add(2)
       .add(3)
       .add(4);
}