英文:
Call a function using expansion pack on a same function
问题
以下是翻译好的部分：
我想能够调用一个函数，该函数接受任意数量的参数，每个参数的值由另一个函数提供：
template <typename T, std::size_t N>
class MyClass
{
public:
void doSomething()
{
doSomethingProxy(std::make_index_sequence<N>());
}
private:
template <std::size_t... I>
void doSomethingProxy(std::index_sequence<I...>)
{
m_obj.doSomething({get()...}); // T::doSomething() 期望一个具有 N 个参数的构造函数的对象，并且我想为该构造函数的每个参数调用 get() 函数 N 次
}
int get() { return 0; }
T m_obj{};
};
然而，执行上述操作会导致错误：
错误：扩展模式 get() 不包含参数包
我认为问题在于 get()... 不依赖于 I，但我不确定如何解决这个问题。
英文:
I would like to be able to call a function over any number of arguments, with each argument's value supplied by another function:
template <typename T, std::size_t N>
class MyClass
{
public:
void doSomething()
{
doSomethingProxy(std::make_index_sequence<N>());
}
private:
template <std::size_t... I>
void doSomethingProxy(std::index_sequence<I...>)
{
m_obj.doSomething({get()...}); // T::doSomething() expects an object whose constructor has N number of arguments, and I would like to call the get() function for each argument of said constructor, N times
}
int get() { return 0; }
T m_obj{};
};
However doing the above results in the error
error: expansion pattern get() contains no parameter packs
I think the issue is that get()... does not depend on I, but I'm not sure how to solve this problem.
答案1
得分: 3
(I,get()) 使用参数包，并导致 get()（逗号操作符，评估两个操作数，返回右操作数）。为了消除关于逗号操作符左操作数无效的警告，您可能需要写成 ((void)I,get())：
#include <cstdint>
#include <utility>
template <typename T, std::size_t N>
class MyClass
{
public:
void doSomething()
{
doSomethingProxy(std::make_index_sequence<N>());
}
private:
template <std::size_t... I>
void doSomethingProxy(std::index_sequence<I...>)
{
m_obj.doSomething({ ((void)I,get())... });
}
int get() { return 0; }
T m_obj{};
};
英文:
(I,get()) is using the parameter pack and results in get() (comma operator, evaluates both operands, returns the rhs). To silence a warning about no effect of lhs of comma operator you might need to write ((void)I,get()):
#include <cstdint>
#include <utility>
template <typename T, std::size_t N>
class MyClass
{
public:
void doSomething()
{
doSomethingProxy(std::make_index_sequence<N>());
}
private:
template <std::size_t... I>
void doSomethingProxy(std::index_sequence<I...>)
{
m_obj.doSomething({ ((void)I,get())... });
}
int get() { return 0; }
T m_obj{};
};
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