#include <iostream>
#include <type_traits>
using namespace std;
 
template <typename T>
T rvalue() { return T(); }
 
template <typename T>
T& lvalue() { static T t; return t; }
 
int main() {
	cout << is_assignable<double, int>::value;
	cout << is_assignable<double, int&>::value;
	cout << is_assignable<double&, int>::value;
	cout << is_assignable<double&, int&>::value;
 
    // rvalue<double>() = rvalue<int>(); // Doesn't compile
    // rvalue<double>() = lvalue<int>(); // Doesn't compile
    lvalue<double>() = rvalue<int>(); // OK
    lvalue<double>() = lvalue<int>(); // OK
	return 0;
}
 

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