[英]How to map different C++ classes to enum class values
我生成消息,每個消息都由一個 object 接收,由enum class
成員選擇:
enum class ReceiverID
{
R1,
R2,
MAX_NUM_RECEIVERS
};
struct Msg
{
ReceiverID _receiverID;
Data _data;
};
接收類存儲在一個數組中。 枚舉成員索引數組以訪問接收 object:
void receive(const Msg& msg)
{
const size_t arrIndex = static_cast<size_t>(msg._receiverID);
if(nullptr == _array[arrIndex])
{
_array[arrIndex] = ??? // How do I associate the enum to the class?
}
_array[arrIndex].processMsg(msg);
}
接收 object 可能丟失。 如果發生這種情況,我想使用枚舉來實例化缺少的 object。 但是,這需要將枚舉值映射到接收 object 類型。
我怎樣才能對每個枚舉 map 一個 class ? (對於所有枚舉)。
如果添加了新枚舉但沒有相應的接收器 class,我想生成編譯器錯誤。
更新
接收對象是多態的,因此具有基礎 class。 數組是:
std::array<Base*, MAX_NUM_RECEIVERS> _array;
(刪除了unique_ptr
以簡化問題)
對於動態創建對象,我們可以 go 使用某種工廠方法,例如:
//In the Base class:
static Base* createReceiver(ReceiverID recvID) //static member function
{
switch (recvID)
{
case ReceiverID::R1: return new R1Receiver();
case ReceiverID::R2: return new R2Receiver();
//...
default: throw std::logic_error("Invalid ReceiverID");
}
}
//...
void receive(const Msg& msg) except(true)
{
const size_t arrIndex = static_cast<size_t>(msg._receiverID);
if(nullptr == _array[arrIndex])
{
_array[arrIndex] = Base::createReceiver(msg._receiverID);
}
_array[arrIndex]->processMsg(msg);
}
而不是全局std::array<Base*, MAX_NUM_RECEIVERS> _array;
然后懶洋洋地按需填寫,我相信正常的做法是在施工時填寫:
std::array<Base*, MAX_NUM_RECEIVERS>& _array() {
//use a method to bypass https://stackoverflow.com/questions/1005685/c-static-initialization-order
static std::array<Base*, MAX_NUM_RECEIVERS> array = make_array();
return array;
}
std::array<Base*, MAX_NUM_RECEIVERS> make_array() {
std::array<Base*, MAX_NUM_RECEIVERS> array;
array[static_cast<size_t>(R1)] = &myR1ProcessorObject();
array[static_cast<size_t>(R2)] = &myR2ProcessorObject();
return array;
}
那么你的接收方法很簡單:
void receive(const Msg& msg)
{
const size_t arrIndex = static_cast<size_t>(msg._receiverID);
assert(arrIndex< MAX_NUM_RECEIVERS);
_array()[arrIndex].processMsg(msg);
}
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