我正在尝试从我的宿主类（ThresholdSensor<>）初始化可变数量的mixins（TrendSensor，EdgeSensor，BaseSensor），这也恰好需要作为构造函数参数，宿主类的成员（BaseSensor::bsd）。我悲惨地完成了两项任务：）
我使用的是c ++ 11，gcc 4.7.1（std :: map没有“emplace”），代码如下：
#include <iostream> // std::cout std::endl
#include <string> // std::string
#include <map> // std::map
using namespace std;
struct BaseSensorData
{
BaseSensorData(const string & _sensorName)
: sensorName(_sensorName)
{}
const string sensorName;
};
class TrendSensor //mixin for BaseSensor
{
public:
TrendSensor( BaseSensorData & bsd , size_t _windowSize , const double & _trainRangefactor)
{
cout << "TrendSensor: " << _windowSize << " " << bsd.sensorName << " " << _trainRangefactor << endl;
}
};
typedef struct{ double trough; double peak; } Edges;
class EdgeSensor //mixin for BaseSensor
{
public:
EdgeSensor( BaseSensorData & bsd , size_t _windowSize , const double _rangeFactor)
{
cout << "EdgeSensor: " << _windowSize << " " << bsd.sensorName << " " << _rangeFactor << endl;
}
};
class CO2Threshold //mixin for ThresholdSensor
{
std::map<std::string , double>thresholds;
public:
CO2Threshold( const double & _toxicThres , const double & _zeroThres , const double & )
{
thresholds["toxic"] = _toxicThres;
thresholds["zero"] = _zeroThres;
cout << "CO2Threshold: " << _toxicThres << " " << thresholds["zero"] << endl;
}
};
class O2Threshold //mixin for ThresholdSensor
{
std::map<std::string , double>thresholds;
public:
O2Threshold( const double & _toxicThres , const double & _lowThres , const double & _elecChemThres )
{
thresholds["toxic"] = _toxicThres;
thresholds["low"] = _lowThres;
thresholds["elecchem"] = _elecChemThres;
cout << "O2Threshold: " << _toxicThres << " " << thresholds["low"] << " " << thresholds["elecchem"] << endl;
}
};
template<typename ThresholdMixin> //CO2Threshold , O2Threshold , or others ...
class ThresholdSensor : public ThresholdMixin //mixin for BaseSensor
{
public:
ThresholdSensor ( BaseSensorData & bsd
, const size_t & _windowSize
, const double & _toxicThres)
: ThresholdMixin
( _toxicThres //3x the same arg
, _toxicThres //just for the sake
, _toxicThres //of this exercise
)
{
cout << "ThresholdSensor: " << _windowSize << " " << bsd.sensorName << " " << endl;
}
};
template<typename ... SensorType>
class BaseSensor : public SensorType ... //to my BaseSensor class
{
BaseSensorData bsd;
public:
BaseSensor(const string& _sensorName , size_t _windowSize , const double d)
:
bsd(_sensorName) //this causes "Wreorder" warning.
,
SensorType( bsd , _windowSize , d )...
{
cout << "BaseSensor: " << _windowSize << " " << bsd.sensorName << " " << endl;
}
};
int main() {
BaseSensor<ThresholdSensor<CO2Threshold> , TrendSensor, EdgeSensor> bs{string("test"),60U , 14.5f};
//BaseSensor<EdgeSensor> bs2;
}
关注BaseSensor，我用gdb运行可执行文件，我意识到没有办法让“bsd”成员首先初始化。 “SensorType”mixins将首先是init。那么我怎样才能首先启动bsd？
其次，逐步执行执行，我意识到执行仅进入“ThresholdSensor”而从未进入“TrendSensor”或“EdgeSensor”。这是为什么？我虽然所有的mixin都会用省略号语法进行评估。 initializer_list会以某种方式帮助初始化吗？如果我包含最终BaseSensor mixins将具有不同数量（和类型）参数的信息并且每个mixin将需要这些参数的不同值，那么initializer_list仍然是建议的解决方案吗？
提前感谢您的帮助
答案 0 :(得分：1)
我不太喜欢以下解决方案，但......
首先：您可以将SensorType类修改为接收（作为构造函数的第一个参数）指针到BaseSensorData而不是引用;例如，TendSensor成为
class TrendSensor //mixin for BaseSensor
{
public:
TrendSensor (BaseSensorData * pBsd, size_t _windowSize,
const double & _trainRangefactor)
{ std::cout << "TrendSensor: " << _windowSize << " "
<< pBsd->sensorName << " " << _trainRangefactor << std::endl; }
};
第二：您可以修改BaseSensor从BaseSensorData（重要：在SensorType...包之前）中导出并删除bsd成员; BaseSensor成为
template <typename ... SensorType>
class BaseSensor : public BaseSensorData, public SensorType ...
{
public:
BaseSensor (const std::string & _sensorName, size_t _windowSize,
const double d)
: BaseSensorData(_sensorName), SensorType(this, _windowSize, d )...
{ std::cout << "BaseSensor: " << _windowSize << " "
<< sensorName << " " << std::endl; }
};
完整的例子如下
#include <iostream> // std::cout std::endl
#include <string> // std::string
#include <map> // std::map
struct BaseSensorData
{
BaseSensorData (const std::string & _sensorName)
: sensorName(_sensorName)
{}
const std::string sensorName;
};
class TrendSensor //mixin for BaseSensor
{
public:
TrendSensor (BaseSensorData * pBsd, size_t _windowSize,
const double & _trainRangefactor)
{ std::cout << "TrendSensor: " << _windowSize << " "
<< pBsd->sensorName << " " << _trainRangefactor << std::endl; }
};
typedef struct { double trough; double peak; } Edges;
class EdgeSensor //mixin for BaseSensor
{
public:
EdgeSensor (BaseSensorData * pBsd, size_t _windowSize,
const double _rangeFactor)
{ std::cout << "EdgeSensor: " << _windowSize << " "
<< pBsd->sensorName << " " << _rangeFactor << std::endl; }
};
class CO2Threshold //mixin for ThresholdSensor
{
private:
std::map<std::string, double> thresholds;
public:
CO2Threshold (const double & _toxicThres, const double & _zeroThres,
const double & )
{
thresholds["toxic"] = _toxicThres;
thresholds["zero"] = _zeroThres;
std::cout << "CO2Threshold: " << _toxicThres << " "
<< thresholds["zero"] << std::endl;
}
};
class O2Threshold //mixin for ThresholdSensor
{
private:
std::map<std::string , double> thresholds;
public:
O2Threshold (const double & _toxicThres, const double & _lowThres,
const double & _elecChemThres)
{
thresholds["toxic"] = _toxicThres;
thresholds["low"] = _lowThres;
thresholds["elecchem"] = _elecChemThres;
std::cout << "O2Threshold: " << _toxicThres << " "
<< thresholds["low"] << " " << thresholds["elecchem"]
<< std::endl;
}
};
template <typename ThresholdMixin> //CO2Threshold , O2Threshold , or others ...
class ThresholdSensor : public ThresholdMixin //mixin for BaseSensor
{
public:
ThresholdSensor (BaseSensorData * pBsd, const size_t & _windowSize,
const double & _toxicThres)
: ThresholdMixin
( _toxicThres, //3x the same arg
_toxicThres, //just for the sake
_toxicThres) //of this exercise
{ std::cout << "ThresholdSensor: " << _windowSize << " "
<< pBsd->sensorName << " " << std::endl; }
};
template <typename ... SensorType>
class BaseSensor : public BaseSensorData, public SensorType ...
{
public:
BaseSensor (const std::string & _sensorName, size_t _windowSize,
const double d)
: BaseSensorData(_sensorName), SensorType(this, _windowSize, d )...
{ std::cout << "BaseSensor: " << _windowSize << " "
<< sensorName << " " << std::endl; }
};
int main()
{
BaseSensor<ThresholdSensor<CO2Threshold>,
TrendSensor, EdgeSensor> bs { std::string("test"), 60U, 14.5f };
//BaseSensor<EdgeSensor> bs2;
}