[英]inheritance of private member variable from class template
我做了一個類模板,如下所示,作為其他類的基礎類,它可以正常工作。
但是我的問題是,即使我將類“ Operation”的“ protected”更改為“ private”,該代碼仍然可以編譯,即使Matmul(繼承類“ Operation”的)正在修改稱為“ edgeIn”的向量,該向量被聲明為“ private” 。
我不明白為什么要允許這樣的事情...編譯器不應該觸發此錯誤消息嗎? (派生類不應修改基類的私有成員)
template<typename T>
class Operation{
private: //Would compile fine even if I change this to 'private!'
class edge{
public:
edge(Tensor<T> tensor, Operation<T> &from, Operation<T> &to) {
this->tensor = tensor;
this->from = from;
this->to = to;
}
Operation<T> from;
Operation<T> to;
Tensor<T> tensor;
};
std::vector<edge> edgeIn; //edges as inputs of this operation
std::vector<edge> edgeOut; //edges as outputs of this operation
private:
//disable copy constructor (NOT ALLOWED)
Operation(Operation<T>& rhs) = default;
//disable move operator (NOT ALLOWED)
Operation<T>& operator=(Operation<T> &rhs) = default;
int operationId;
};
template<typename T>
class Matmul: public Operation<T>{
public:
Matmul(std::initializer_list<std::pair<Tensor<T>, Operation<T>>> args);
};
template<typename T>
//from Operation<T>, to This operation
Matmul<T>::Matmul(std::initializer_list<std::pair<Tensor<T>, Operation<T>>> args){
for(auto elem: args){
typename Operation<T>::edge info{elem.first, elem.second, *this};
this->edgeIn.emplace_back(info); //modifying member of base class
}
}
在您顯示的代碼中,它是允許的,因為它沒有錯。 這是一個更簡單的示例:
template <class Ty>
class base {
int i; // private
};
template <class Ty>
class derived : base {
void set(int ii) { i = ii; }
};
此時,如果您寫
derived<int> di;
di.set(3); // illegal: i is not accessible
如您所料,您將收到訪問錯誤。
但是原始模板沒有錯,因為代碼可以這樣做:
template <>
class base<int> {
public:
int i;
};
現在你可以寫
derived<int> di;
di.set(3);
沒關系,因為i
在base<int>
公開。 你還是不能寫
derived<double> dd;
dd.set(3); // illegal: i is not accessible
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