不明确的函数调用到C ++基类 [英] Ambiguous Function Calls to C++ base classes

问题描述

我想创建一个可变模板类，为类型列表中的每个类提供一个方法。下面显示一个例子，它为类型串中的每个类创建一个 print 方法：

I'm trying to create a variadic templated class which provides a method for each class in the typelist. An example is shown below which creates a print method for every class in the typelist:

#include <iostream>
#include <string>

// Helper class providing a function call
template <typename T>
class PrintHelper
{
public:
    void print(const T& t) { std::cout << t << std::endl; }
};

// Provides a print method for each type listed
template <typename... Ts>
class Printer : public PrintHelper<Ts>...
{};

int main()
{
    Printer<int, std::string> p;
    p.print(std::string("Hello World")); // Ambiguous Call
}

注释行会导致GCC 4.6.3错误在注释行。

The commented line results in an error from GCC 4.6.3 on the commented line. What is the correct way to resolve the ambiguity or should I be looking at a different design?

推荐答案

我不喜欢回答的问题是什么是解决歧义的正确方法？我自己的问题，但是我从这里的评论创建了以下解决方案。它将所有 print 函数带入范围，并允许对所有函数进行C ++重载解析。

I don't like answering my own question but I've created the following solution from the comments here. It brings all print functions into scope and allows for C++ overload resolution on all of the functions.

#include <iostream>
#include <string>

// Helper class providing a function call
template <typename T>
class PrintHelper
{
public:
    void print(const T& t) { std::cout << t << std::endl; }
};

// Provides a print method for each type listed
template <typename... Ts>
class Printer
{};

template<typename T>
class Printer<T> : public PrintHelper<T>
{
public:
    using PrintHelper<T>::print;
};

template<typename T, typename... Ts>
class Printer<T, Ts...>: public PrintHelper<T>, public Printer<Ts...>
{
public:
    using PrintHelper<T>::print;
    using Printer<Ts...>::print;
};

int main()
{
    Printer<int, std::string> p;
    p.print("Hello World"); // Not an ambiguous Call
}

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