Why does initialization of int by parenthesis inside class give error?

I was trying to initialize non-static int member variable of class in c++11. I encountered this in Scott Meyers book (9th release) at page 50. The book says error but doesn't say why. May be I am not able to read between the lines. Is there reason why this fails. I just wanted to know the reason behind the fail.

#include <iostream>

class A {
   public:
    A(){};

   private:
    int x = 1; // fine
    int y{3}; // fine
    int z(0); // error
};

int main() {
    int x(5); // this works as well

    A a;
    std::cout << x << std::endl;
}