可变参数模板与模板函数名称和传递参数和返回值 [英] variadic templates with template function names and passing arguments and return values around
问题描述
此问题,我一直在试图创建一个模板函数,调用其mixins的所有相同命名的方法。这在上一个问题中已经完成和验证。
现在我试图获得SensorType ::
的返回值分析:
#include< iostream>
#include< string>
struct EdgeSensor
{
void update(int i){std :: cout< EdgeSensor :: update< i<< std :: endl; }
void updat2(const int i){std :: cout< EdgeSensor :: updat2< i<< std :: endl; }
std :: string printStats(){std :: cout<< EdgeSensor :: printStats< std :: endl;
return std :: string(EdgeSensor :: printStats); }
};
struct TrendSensor
{
void update(int i){std :: cout< TrendSensor :: update< i<< std :: endl; }
void updat2(const int i){std :: cout< TrendSensor :: updat2< i<< std :: endl; }
std :: string printStats(){std :: cout<< TrendSensor :: printStats< std :: endl;
return std :: string(TrendSensor :: printStats); }
};
template< class T,void(T :: *)(const int)>
struct Method {};
template< typename ... SensorType>
class BaseSensor:public SensorType ... // to my BaseSensor class
{
template< class T,void(T :: * M)(const int)>
int runSingle(Method< T,M>,const int i){
(this-> * M)(i);
return 0;
}
template< class ... Ts>
void runAll(const int i){
int run [sizeof ...(Ts)] = {runSingle(Ts {},i)...}
(void)run;
}
public:
void update(){
runAll< Method< SensorType,& SensorType :: update> ...>(2)
}
void updat2(){
const int k = 3;
runAll< Method< SensorType,& SensorType :: updat2> ...>(k);
}
void printStats(){
// runAll< Method< SensorType,& SensorType :: printStats> ...>
}
};
int main(){
{
BaseSensor< EdgeSensor,TrendSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
{
BaseSensor< EdgeSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
}
上述编译并运行正常。问题是:如何从 BaseSensor中运行mixin
? SensorType :: printStats()
方法收集返回值(std :: strings) :printStats()
如果我尝试创建一个二进制版本的 run *
函数和方法
模板,我无法使其编译。说我做了:
模板< class T,void(T :: *)()>
struct Method2 {};
template< class T,void(T :: * M)()>
int runSingle2(Method2< T,M>){
(this-> * M)
return 0;
}
template< class ... Ts>
void runAll2(){
std :: string s;
int run [sizeof ...(Ts)] = {s = runSingle2(Ts {})...}
(void)run;
std :: cout<< s =< s < std :: endl;
}
public:
void update(){
int k = 4;
runAll< Method< SensorType,& SensorType :: update> ...>(k);
}
void printStats(){
runAll2< Method2< SensorType,& SensorType :: printStats> ...>
}
};
这不会编译
g ++ -Wall -Wextra -g -std = c ++ 11 -c -oobj_dbg / main.oppmain.cpp
main.cpp: void BaseSensor< SensorType> :: printStats()[with SensorType = EdgeSensor,TrendSensor]':
main.cpp:65:20:从这里需要
main.cpp:58:8:error:could不将模板参数'& EdgeSensor :: printStats'转换为'void(EdgeSensor :: *)()'
make:*** [obj_dbg / main.opp]错误1
$ c因此,我如何从 SensorType :: printStats()
获取返回值?
解决方案不确定是否可以使用c ++ 11,如果是这样,那么我认为这是最简单的?
#include< iostream>
#include< string>
struct EdgeSensor
{
void update(int i){std :: cout< EdgeSensor :: update< i<< std :: endl; }
void updat2(const int i){std :: cout< EdgeSensor :: updat2< i<< std :: endl; }
std :: string printStats(){std :: cout<< EdgeSensor :: printStats< std :: endl;
return std :: string(EdgeSensor :: printStats); }
};
struct TrendSensor
{
void update(int i){std :: cout< TrendSensor :: update< i<< std :: endl; }
void updat2(const int i){std :: cout< TrendSensor :: updat2< i<< std :: endl; }
std :: string printStats(){std :: cout<< TrendSensor :: printStats< std :: endl;
return std :: string(TrendSensor :: printStats); }
};
template< typename ... SensorType>
class BaseSensor:public SensorType ... // to my BaseSensor class
{
public:
void update(){
auto v = {(static_cast< SensorType *>(this) - > update(1),0)...} // *
(void)v;
}
void updat2(){
const int k = 3;
auto v = {(static_cast< SensorType *>(this) - > updat2(k),0)...} // *
(void)v;
}
void printStats(){
auto v = {static_cast< SensorType *>(this) - > printStats()...}
for(auto s:v){
std :: cout< s < std :: endl;
}
}
};
int main(){
{
BaseSensor< EdgeSensor,TrendSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
{
BaseSensor< EdgeSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
}
- 注意:在这里使用gcc扩展,但我认为你正在使用gcc,所以应该是好的
following from this question, I have been trying to create a template function that calls all same-named methods of its mixins. This has been done and verified in the previous question.
Now I am attempting to get the return value of SensorType::
Analytically:
#include<iostream>
#include <string>
struct EdgeSensor
{
void update(int i) { std::cout << "EdgeSensor::update " << i << std::endl; }
void updat2(const int i ) { std::cout << "EdgeSensor::updat2" << i << std::endl; }
std::string printStats() { std::cout << "EdgeSensor::printStats" << std::endl;
return std::string("EdgeSensor::printStats"); }
};
struct TrendSensor
{
void update(int i ) { std::cout << "TrendSensor::update" << i << std::endl; }
void updat2(const int i ) { std::cout << "TrendSensor::updat2" << i << std::endl; }
std::string printStats() { std::cout << "TrendSensor::printStats" << std::endl;
return std::string("TrendSensor::printStats"); }
};
template <class T, void (T::*)(const int)>
struct Method { };
template<typename ... SensorType>
class BaseSensor : public SensorType ... //to my BaseSensor class
{
template <class T, void(T::*M)(const int)>
int runSingle(Method<T, M> , const int i) {
(this->*M)(i);
return 0;
}
template <class... Ts>
void runAll(const int i) {
int run[sizeof...(Ts)] = { runSingle(Ts{},i)... };
(void)run;
}
public:
void update() {
runAll<Method<SensorType, &SensorType::update>...>(2);
}
void updat2() {
const int k = 3;
runAll<Method<SensorType, &SensorType::updat2>...>(k);
}
void printStats() {
// runAll<Method<SensorType, &SensorType::printStats>...>();
}
};
int main() {
{
BaseSensor<EdgeSensor,TrendSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
{
BaseSensor<EdgeSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
}
The above compiles and runs fine. The problem is: how can I gather the return values (std::strings) from running the mixin SensorType::printStats()
methods in BaseSensor::printStats()
?
If I try to create a 2ndary version of the run*
functions and the Method
template, I fail to make it compile. Say I did:
template <class T, void (T::*)()>
struct Method2 { };
template <class T, void(T::*M)()>
int runSingle2(Method2<T, M>) {
(this->*M)();
return 0;
}
template <class... Ts>
void runAll2() {
std::string s;
int run[sizeof...(Ts)] = { s = runSingle2(Ts{})... };
(void)run;
std::cout << "s=" << s << std::endl;
}
public:
void update() {
int k = 4;
runAll<Method<SensorType, &SensorType::update>...>(k);
}
void printStats() {
runAll2<Method2<SensorType, &SensorType::printStats>...>();
}
};
This does not compile saying
g++ -Wall -Wextra -g -std=c++11 -c -o "obj_dbg/main.opp" "main.cpp"
main.cpp: In instantiation of ‘void BaseSensor<SensorType>::printStats() [with SensorType = EdgeSensor, TrendSensor]’:
main.cpp:65:20: required from here
main.cpp:58:8: error: could not convert template argument ‘&EdgeSensor::printStats’ to ‘void (EdgeSensor::*)()’
make: *** [obj_dbg/main.opp] Error 1
So HOW can I grab the return values from SensorType::printStats()
?
解决方案 Not sure if you can use c++11, if so, then I think this is the easiest?
#include <iostream>
#include <string>
struct EdgeSensor
{
void update(int i) { std::cout << "EdgeSensor::update " << i << std::endl; }
void updat2(const int i ) { std::cout << "EdgeSensor::updat2" << i << std::endl; }
std::string printStats() { std::cout << "EdgeSensor::printStats" << std::endl;
return std::string("EdgeSensor::printStats"); }
};
struct TrendSensor
{
void update(int i ) { std::cout << "TrendSensor::update" << i << std::endl; }
void updat2(const int i ) { std::cout << "TrendSensor::updat2" << i << std::endl; }
std::string printStats() { std::cout << "TrendSensor::printStats" << std::endl;
return std::string("TrendSensor::printStats"); }
};
template<typename ... SensorType>
class BaseSensor : public SensorType ... //to my BaseSensor class
{
public:
void update() {
auto v = { (static_cast<SensorType*>(this)->update(1), 0)... }; // *
(void) v;
}
void updat2() {
const int k = 3;
auto v = { (static_cast<SensorType*>(this)->updat2(k), 0)... }; // *
(void) v;
}
void printStats() {
auto v = { static_cast<SensorType*>(this)->printStats()... };
for (auto s : v) {
std::cout << s << std::endl;
}
}
};
int main() {
{
BaseSensor<EdgeSensor,TrendSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
{
BaseSensor<EdgeSensor> ets;
ets.update();
ets.updat2();
ets.printStats();
}
}
- NOTE: I am using a gcc extension here, but I think you are using gcc, so it should be okay
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