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c++c++11rvalue-referencelvalue

Can a member function returns a modifiable lvalue reference to an rvalue object?

I have a bit confusion about this code:

struct A
{
    A& bar()&&;
};

A& A::bar()&&
{
    std::cout << "A::bar()&&\n";
    return *this;
}

int main()
{
    A{}.bar();// called by an rvalue
}

So what I understand is that bar can be called only by a modifiable-rvalue. Until this it is OK. But how can bar return a non-constant lvalue reference to that rvalue?

  • How bar() binds and returns a modifiable lvalue reference to that rvalue object?
Solution

  • The reason is that the this pointer for a class C can be either C* or const C* - not C& * or C&& * (those aren't actual types; you can't declare a C& * ptr). So, even when your method runs for an rvalue instance of class A, you get one of those two (GodBolt). And when you apply the * operator, you get an lvalue, not an rvalue.