[英]How do I create an std::tuple<> from a variadic template parameter?
I have a class that is declared with this template: template <typename ...Args>
.我有一个用这个模板声明的类: template <typename ...Args>
。 In it, I have a list declared as std::vector<std::tuple<Args...>> vec;
在其中,我有一个声明为std::vector<std::tuple<Args...>> vec;
to store data entries specified by the template.存储模板指定的数据条目。 I also have a function declared as follows:我还有一个函数声明如下:
void AddVertex(Args... data)
{
// vec.push_back(std::tuple<Args...>(data));
}
In this function, I want to add a tuple of Args... to the vector.在这个函数中,我想向向量添加一个 Args... 元组。 Is this possible?这可能吗? I have tried using the code in the comment, but the compiler gives me an error saying that "the parameter pack must be expanded in this context".我已经尝试使用注释中的代码,但是编译器给了我一个错误,说“必须在此上下文中扩展参数包”。
This solution doesn't work, because the template argument of the tuple is already expanded.此解决方案不起作用,因为元组的模板参数已经展开。
You need to expand both:您需要扩展两者:
Args...
)模板参数包( Args...
)and和
data...
):函数参数包( data...
):so it should be:所以应该是:
vec.push_back(std::tuple<Args...>(data...));
Or shorter form, use make_tuple
:或者更短的形式,使用make_tuple
:
vec.push_back(std::make_tuple(data...));
As hinted by the compiler, you need to expand the parameter pack data
, so this should work:正如编译器所暗示的,您需要扩展参数包data
,所以这应该可以工作:
void AddVertex(Args... data)
{
vec.push_back(std::tuple<Args...>(args...));
}
Also, consider using emplace_back
instead:另外,请考虑使用emplace_back
代替:
void AddVertex(Args... data)
{
vec.emplace_back(args...);
}
Both of the above functions will copy every argument and thus are not idiomatic C++.上述两个函数都将复制每个参数,因此不是惯用的 C++。 This may or may not be an issue to you.这对您来说可能是也可能不是问题。 To avoid this do something like为了避免这种情况,请执行以下操作
template <typename... T>
void AddVertex(T&&... args)
{
vec.emplace_back(std::forward<T>(args)...);
}
which is a little more verbose, but will avoid those unnecessary copies.这有点冗长,但会避免那些不必要的副本。
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