将可变参数模板参数解压缩到初始化程序列表中 [英] Unpacking variadic template parameters into initializer list

问题描述

我目前正在尝试实现通用的初始化程序，以减小代码库的大小.但是，在某一时刻，我的代码看起来像这样:

I am currently trying to implement a general initializer to reduce the size of our codebase. At one point however, my code looked like this:

template<typename T, typename Arg1, typename Arg2>
T* ManageDevice(Arg1 arg1, Arg2 arg2)
{
    auto device = new T{ arg1, arg2 };
    // More operations on device
    return device;
}

template<typename T, typename Arg1, typename Arg2, typename Arg3>
T* ManageDevice(Arg1 arg1, Arg2 arg2, Arg3 arg3)
{
    auto device = new T{ arg1, arg2, arg3 };
    // More operations on device
    return device;
}

template<typename T, typename Arg1, typename Arg2, typename Arg3, typename Arg4>
T* ManageDevice(Arg1 arg1, Arg2 arg2, Arg3 arg3, Arg4 arg4)
{
    auto device = new T{ arg1, arg2, arg3, arg4 };
    // More operations on device
    return device;
}

哪个开始不那么优雅了.据我了解，可变参数模板似乎是解决此问题的方法.但是我不知道如何将其应用于我的情况.

Which starts to be less elegant. From my understanding, variadic templates seems to be the way to solve this issue. But I don't understand how this can be applied to my situation.

我更喜欢这样的东西:

T* ManageDevice(Args... args)
{
    // The function I want
    // Unpack as a std::initializer_list
    auto allArguments = unpackAll(); 

    auto device = new T{ allArguments };
    // More operations on device
    return device;
}

关于应如何实现unpackAll()的任何建议?谢谢.

Any suggestion on how unpackAll() should be implemented? Thanks.

推荐答案

auto device = new T{ allArguments };

只是需要

auto device = new T{ args... };

在 T {args ...} 中 args ... 将参数包扩展为 arg0，arg1，...，argn 为您服务.

In T{ args... } args... will expand the parameter pack to arg0, arg1, ..., argn for you.

您可以看到它与之配合使用

You can see this working with

template <typename... Args>
std::vector<int> make_vector(Args... args)
{
    return {args...};
}

int main()
{
    auto foo = make_vector(1,2,3,4);
    for (auto e : foo)
        std::cout << e << " ";
}

---

编辑以添加完善的转发版本

---

Edit to add perfect forwarding version

template <typename... Args>
std::vector<int> make_vector(Args&&... args)
{
    return {std::forward<Args>(args)...};
}

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