[英]How to map different C++ classes to enum class values
我生成消息,每个消息都由一个 object 接收,由enum class
成员选择:
enum class ReceiverID
{
R1,
R2,
MAX_NUM_RECEIVERS
};
struct Msg
{
ReceiverID _receiverID;
Data _data;
};
接收类存储在一个数组中。 枚举成员索引数组以访问接收 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 可能丢失。 如果发生这种情况,我想使用枚举来实例化缺少的 object。 但是,这需要将枚举值映射到接收 object 类型。
我怎样才能对每个枚举 map 一个 class ? (对于所有枚举)。
如果添加了新枚举但没有相应的接收器 class,我想生成编译器错误。
更新
接收对象是多态的,因此具有基础 class。 数组是:
std::array<Base*, MAX_NUM_RECEIVERS> _array;
(删除了unique_ptr
以简化问题)
对于动态创建对象,我们可以 go 使用某种工厂方法,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;
然后懒洋洋地按需填写,我相信正常的做法是在施工时填写:
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简单:
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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