C++核心準(zhǔn)則C.138:使用using為派生類生成重載函數(shù)集合?

C.138: Create an overload set for a derived class and its bases with?using

C.138:使用using為派生類生成重載函數(shù)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聲明，派生類中的成員函數(shù)會隱藏整個繼承來的

重載函數(shù)集合。

Example, bad(反面示例)

#include?
class?B?{
public:
????virtual?int?f(int?i)?{
????????std::cout?<????}
????virtual?double?f(double?d)?{
????????std::cout?<????}
????virtual?~B()?=?default;
};

class?D:?public?B?{
public:
????int?f(int?i)?override?
????{
????????std::cout?<????}
};

int?main()
{
????D?d;
????std::cout?<????std::cout?<}

Example, good(范例)

class?D:?public?B?{
public:
????int?f(int?i)?override?
????{
????????std::cout?<????}
????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,

本條款對虛函數(shù)和非虛函數(shù)都有效。對于可變基類，C++17引入using聲明的可變形式。

template?
struct?Overloader?:?Ts...?{
????using?Ts::operator()...;?//?exposes?operator()?from?every?base
};

Enforcement（實施建議）

Diagnose name hiding

檢出名稱隱藏。

原文鏈接：

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c138-create-an-overload-set-for-a-derived-class-and-its-bases-with-using

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