C++ 嵌套模板 : inaccessible static method

Question

我在以下代码中遇到了一个奇怪的(或者可能不是)错误:

template<typename T>
class Registrer {
public:
    Registrer() {
        Registry::register(T::instance);
    }
};

template<typename T>
class RegisteringClass {
private:
    static const Registrer<T> REGISTRER;
public:
    RegisteringClass () { Q_UNUSED(REGISTRER); /* force static instantiation     */ }
    static const WhatEver *instance() { static T INSTANCE; return &INSTANCE; }
};

template<typename T>
const Registrer<T> RegisteringClass<T>::REGISTRER;

class Something : public WhatEver, RegistringClass<Something> {
}

当 instance 方法在模板中时，出现以下错误 (gcc)

error: 'static const WhatEver* RegisteringClass<T>::instance() [with T = Something]' is inaccessible
    static const WhatEver*instance() { static T INSTANCE; return &INSTANCE; }
error: within this context
     Registry::register(T::instance);
In instantiation of 'static const WhatEver* RegisteringClass<T>::instance() [with T = Something]':

而当 instance() 在 Something 中时，一切都很好。

我是否遗漏了一些微妙的语法？或者这是模板限制？

Answer 1

派生类时，'private'是默认的；否则，您必须为派生自的每个类使用“public”或“protected”关键字:

class C : public A, public B 
{
     void f(); 
};