constexpr成员函数给出C2131[重复]

我已经理解了 const 和 constexpr 和他们的应用程序,但我无法得到它的以下错误:

// .hpp file
class MyClass {
public:
    constexpr double Square(double toBeSquared);
    static constexpr double Cube(double x);
    double ProcessRoutine();
};

// .cpp file
constexpr double alternative_square_routine(double x)
{
    return x * x;
}

double MyClass::Square(double toBeSquared)
{
    return x * x;
}

double MyClass::Cube(double x)
{
    return x * x * x;
}

double MyClass::ProcessRoutine()
{
    // C2131: expression did not evaluate to a constant
    constexpr double square_const = Square(10.0);
    // This is fine:
    const double another_square = Square(5.0);
    // This is also fine:
    constexpr double another_square_again = alternative_square_routine(5.0);
    // Even this is fine:
    constexpr double cube = Cube(3.0);
}

MSVC告诉我,这涉及到 this 指针,在尝试Codiva.io中的代码时(我猜它使用GCC)会给出以下输出:

error: constexpr variable 'square_const' must be initialized by a constant expression

问题出在哪里?