Question

According to what I know it is not valid to bind a lvalue into a rvalue reference.
And secondly, a lvalue expression is recognizable by the fact it can be prefix by adress-of operator, (&)

I’m a little bit in trouble if this two sentences arecorrect with the following codes :

 #include<iostream>

struct Foo
{
    Foo(Foo&& other)
    {
        std::cout << "move ctor called";
    }

    Foo(const Foo& other)
    {
        std::cout << "copy ctor called";
    }

    Foo(){}
};

Foo return_foo()
{
    Foo f;
    return f;
}


void main()
{  
    Foo f = return_foo(); // Move ctor is called, but return_foo() is a lvalue ?? 
    std::cin.ignore();    
}

Where I am wrong ?

Answer 1

return_foo() returns a prvalue (because it returns unnamed temporary object). Quote from §3.10/1, emphasis mine:

A prvalue (“pure” rvalue) is an rvalue that is not an xvalue. [
Example: The result of calling a function whose return type is not a
reference is a prvalue. The value of a literal such as 12, 7.3e5, or
true is also a prvalue. —end example ]