Why cast expression to rvalue reference to function is lvalue?

Question

At here,cppreference-lvalue,I found that

Cast expression to rvalue reference to function is lvalue.

I was curious, so I carried out the following experiment:

#include <iostream>

using namespace std;


typedef void (&&funr) (int);
typedef void (&funl) (int);

void test(int num){
    cout<<num<<endl;//output:20
}

void foo(funr fun){
    fun(10);
}

void foo(funl fun){
    fun(20);//call this
}

template <typename T> void foo(T&& fun){
    cout<<is_same<T,void(&)(int)>::value<<endl;//true, it is lvalue. 
    cout<<is_same<T,void(int)>::value<<endl;//false, it isn't rvalue.
}
int main()
{

   foo(static_cast<void(&&)(int)>(test));
   return 0;
}

the fact that so.

Why cast expression to rvalue reference to function is lvalue? Is it because a function type is no need to move semantics or something else? Or I understand this word wrong.

Cast expression to rvalue reference to function is lvalue

Answer 1

It follows from the definition of value categories in C++11 3.10/1 (emphasis mine):

• An lvalue (...) designates a function or an object. ...

• An xvalue (an “eXpiring” value) also refers to an object, ...

• An rvalue (...) is an xvalue, a temporary object (12.2) or subobject thereof, or a value that is not associated with an object.

• A prvalue (“pure” rvalue) is an rvalue that is not an xvalue. ...

Notice that only the lvalue category can be a function, all the others are values or objects only.

It's also echoed in 5.2.9/1:

The result of the expression static_cast<T>(v) is the result of converting the expression v to type T. If T is an lvalue reference type or an rvalue reference to function type, the result is an lvalue; if T is an rvalue reference to object type, the result is an xvalue; otherwise, the result is a prvalue. ...

As for the why of it, I can of course only guess (not being part of the standardisation committee). But my guess is that it would make no sense to have rvalues of function type—a function can never be a temporary, it can never be at or near the end of its lifetime.