How to determine programmatically if an expression is rvalue or lvalue in C++?

Question

What\'s the best way to determine if an expression is a rvalue or lvalue in C++? Probably, this is not useful in practice but since I am learning rvalues and lvalues I thoug

Answer 1

I solved the above question using two overloaded template functions. The first takes as input a reference to a lvalue and return true. Whereas the second function uses a reference to rvalue. Then I let the compiler match the correct function depending on the expression passed as input.

Code:

#include 

template 
constexpr bool is_lvalue(T&) {
    return true;
}

template 
constexpr bool is_lvalue(T&&) {
    return false;
}

int main()
{
    std::string a = std::string("Hello");
    std::cout << "Is lValue ? " << '\n';
    std::cout << "std::string() : " << is_lvalue(std::string()) << '\n';
    std::cout << "a : " << is_lvalue(a) << '\n';
    std::cout << "a+b : " << is_lvalue(a+ std::string(" world!!! ")) << '\n';
} 

Output:

Is Lvalue ? 
std::string() : 0
a : 1
a+b : 0