相关疑难解决方法(0)

当我运行此代码时:

struct X {
    int a;
};

struct Y : public X {};

X x = {0};
Y Y = {0};

我明白了:

error: could not convert ‘{0}’ from ‘<brace-enclosed initializer list>’ to ‘Y’

为什么大括号初始化适用于基类而不适用于派生类？