c ++ 11：从模板函数构建std :: tuple [英] c++11: building a std::tuple from a template function

问题描述

我有以下功能：

template<class T>
T Check(int index);

如何写一个函数 CheckTuple ，在给定一个元组类型的情况下，使用对检查 c>

How can I write a function, CheckTuple, which, given a tuple type, populates a tuple with calls to Check?

例如：

CheckTuple< std::tuple<int, float, std::string> >()

将返回以下元组：

std::make_tuple( Check<int>(1), Check<float>(2), Check<std::string>(3) )

我看到的其他问题涉及解包给定的元组，而不是以这种方式构建。

The other questions I see involve unpacking a given tuple, not building one up this way.

推荐答案

使用C ++ 14的 integer_sequence 。如果您没有可用的资源，请这是一个C ++ 11实现由 Jonathan Wakely 撰写。

Implementing what you're looking for becomes pretty simple using C++14's integer_sequence. If you don't have that available, here's a C++11 implementation written by Jonathan Wakely.

template<typename Tuple, int... I>
Tuple CallCheck(std::integer_sequence<int, I...>)
{
    return std::make_tuple(Check<typename std::tuple_element<I, Tuple>::type>(I)...);
}

template<typename Tuple>
Tuple CheckTuple()
{
    return CallCheck<Tuple>(std::make_integer_sequence<int, std::tuple_size<Tuple>::value>());
}

// Use it as 
auto tup = CheckTuple<std::tuple<int, float, std::string>>();

现场演示

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