Show how to use ref qualifiers to prevent dangling references to member variable

getters_with_ref_qualifiers.cpp

// Show how to use ref qualifiers to prevent dangling references to member variables.

struct S {
    const int& f() const& { return n_;}

    const int& h() & { return n_; }

    const int& g() && { return n_; }

    const int& l() const & { return n_; }
    const int& l() && = delete;

    int n_ = 0;
};

int main() {
    S s;
    const S ks;

    // Problematic because callable on both lvalues and rvalues.
    // Callable on rvalues because const lvalue refs accept temporaries (and extend their lifetime).
    s.f();
    ks.f();
    S().f();  // returned reference dangles

    // Safe because callables on lvalues only.
    s.h();
    // does not compile (usual rules about const vs non-const member functions)
    // ks.h();
    // does not compile because non-const lvalue ref do not bind to temporaries
    // S().h();

    // Problematic because callable on rvalue only.
    // does not compile because rvalue ref does not bind to lvalue
    // s.g();
    // ks.g();
    S().g();

    // Safe because callable on lvalue only.
    s.l();
    ks.l();
    // does not compile because overload deleted
    // S().l();
}