[英]How to store arguments list to vector?
如何將可變參數構造函數 arguments 存儲到向量?
我失敗的嘗試示例:
class Combo
{
public:
template <class... Args>
Combo(Args... args)
{
// this->keys_.push_back(args...);
// this->keys_.push_back(args)...;
// this->keys_.push_back(std::forward<Args>(args...));
//for (uint8_t arg : args...)
// this->keys_.push_back(arg);
// ???
}
private:
std::vector<uint8_t> keys_;
};
for(auto &&i: {args...}) keys.push_back(std::move(i));
(keys.push_back(args), ...);
template<class... Args> Combo(Args... args): keys_{uint8_t(args)...} {}
#include <vector>
#include <utility> // std::forward
class Combo
{
public:
template <class... Args>
Combo(Args&&... args)
{
keys_.reserve(sizeof...(Args)); // reserve memory for unwanted reallocation
(keys_.emplace_back(std::forward<Args>(args)), ...);
}
private:
std::vector<uint8_t> keys_;
};
但是,這將允許傳遞uint8_t
以外的類型,並且對於那些可以隱式轉換為uint8_t
的類型,將進行隱式轉換。
這將不是所需的行為。 因此,我建議static_assert
如下。
#include <type_traits> // std::is_same_v
template <class... Args>
Combo(Args&&... args)
{
// to make sure that the args all are of type `uint8_t`
static_assert((std::is_same_v<uint8_t, Args> && ...), "Args should be uint8_t");
keys_.reserve(sizeof...(Args)); // reserve some memory for unwanted reallocation
(keys_.emplace_back(std::forward<Args>(args)), ...);
}
現在這會給您以下錯誤
Combo obj{ 1, 2, 3, 4.f };
// ^^^^ --> float
你可以寫:
template <class... Args>
Combo(Args... args)
{
(keys_.push_back(args), ...);
}
template<typename... Args>
Combo(Args &&... args): keys_ { std::forward<Args>(args)... } {}
甚至更好
Combo(std::initializer_list<uint8_t> keys): keys_(keys) {}
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