#include <cassert>
#include <type_traits>

class Counter {
    int value_ = 0;
public:
    Counter& set(int value) & {
        static_assert(std::is_same<decltype(this), Counter*>::value, "mutable this");
        value_ = value;
        return *this;
    }
    int value() const {
        static_assert(std::is_same<decltype(this), const Counter*>::value, "const this");
        return value_;
    }
    bool same_object(const Counter& other) const { return this == &other; }
};

int main() {
    Counter counter;
    Counter& result = counter.set(2).set(5);
    const Counter& view = counter;
    assert(&result == &counter);
    assert(view.value() == 5);
    assert(view.same_object(result));
}