Can rvalue references be passed on as const references?

Question

Consider the following example struct:

struct A {
    int i;

    void init(const A &a)
    {
        this->i = a.i;
    }

    A(int i)
    {
        this->i = i;
    }

    A(const A &a) = delete;
    A &operator=(const A &a) = delete;

    A(A &&a)
    {
        init(a); // Is this allowed?
    }

    A &operator=(A &&a)
    {
        init(a); // Is this allowed?
        return *this;
    }
};

The rvalue reference A &&a is passed on to a function accepting a const A &a, i.e. a constant lvalue reference. Is this allowed and resulting in well defined behaviour in C++?

Answer 1

Yes, it is allowed.

Note, that value category of the expression a is lvalue, even though a's declared type is rvalue reference.

Furthermore, if you create an rvalue from a with std::move, your code is still well-formed, as an rvalue can be bound to a const lvalue reference:

init(std::move(a)); // std::move(a) is an rvalue (to be precise, xvalue), but still OK