C.138: Create an overload set for a derived class and its bases with using
C.138:使用using为派生类生成重载函数集合
Reason(原因)
Without a using declaration, member functions in the derived class hide the entire inherited overload sets.
如果不使用using声明，派生类中的成员函数会隐藏整个继承来的
重载函数集合。
Example, bad(反面示例)
#include <iostream>
class B {
public:
virtual int f(int i) {
std::cout << "f(int): "; return i;
}
virtual double f(double d) {
std::cout << "f(double): "; return d;
}
virtual ~B() = default;
};
class D: public B {
public:
int f(int i) override
{
std::cout << "f(int): "; return i + 1;
}
};
int main()
{
D d;
std::cout << d.f(2) << '\n'; // prints "f(int): 3"
std::cout << d.f(2.3) << '\n'; // prints "f(int): 3"
}
Example, good(范例)
class D: public B {
public:
int f(int i) override
{
std::cout << "f(int): "; return i + 1;
}
using B::f; // exposes f(double)
};
Note(注意）
This issue affects both virtual and nonvirtual member functions
For variadic bases, C++17 introduced a variadic form of the using-declaration,
本条款对虚函数和非虚函数都有效。对于可变基类，C++17引入using声明的可变形式。
template <class... Ts>
struct Overloader : Ts... {
using Ts::operator()...; // exposes operator() from every base
};
Enforcement（实施建议）
Diagnose name hiding
检出名称隐藏。
原文链接：
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c138-create-an-overload-set-for-a-derived-class-and-its-bases-with-using
觉得本文有帮助？欢迎点赞并分享给更多的人。
阅读更多更新文章，请关注微信公众号【面向对象思考】
