variadic templates with template function names for c++11 - c++

Question

following this question , I am trying to avoid copy-pasting some code related to calling all of the same-named methods of the mixins of the class BaseSensor.
in sensor.hpp
struct EdgeSensor //a mixin
{
void update(){}
void printStats() {}
};
struct TrendSensor //another mixin
{
void update(){}
void printStats() {}
};
template<typename ... SensorType>
class BaseSensor : public SensorType ... //to my BaseSensor class
{
void update() /*{ what goes in here??? }*/
void printStats() /*{ what goes in here??? }*/
};
in sensor.t.hpp
template<typename ... SensorType>
void BaseSensor<SensorType...>::update()
{
int arr[] = { (SensorType::update(), 0)..., 0 };
(void)arr;
}
template<typename ... SensorType>
void BaseSensor<SensorType...>::printStats()
{
int arr[] = { (SensorType::printStats(), 0)..., 0 };
(void)arr;
}
in main.cpp
int main(int , const char **)
{
{
BaseSensor<EdgeSensor,TrendSensor> ets;
ets.update();
ets.printStats();
}
{
BaseSensor<EdgeSensor> ets;
ets.update();
ets.printStats();
}
}
The above code executes the update() of all the mixins in turn, before going on to execute all the printStats() from all the mixins as well.
I wonder if it is somehow possible to avoid duplicating the implementation of BaseSensor::update() and BaseSensor::printStats() and create a generic (template) function that accepts the name of the target function to execute across all the mixins:
For example, I could create a method runAll()
template<typename ... SensorType>
class BaseSensor : public SensorType ... //to my BaseSensor class
{
void update() /*{ what goes in here??? }*/
void printStats() /*{ what goes in here??? }*/
template<typename FnName>
void runAll(FnName f)
{
int arr[] = { (SensorType::f(), 0)..., 0 };
(void)arr;
}
};
How would I call it then from BaseSensor::update() and BaseSensor::printStats(). I have attempted to use
void update() { runAll<update>(); }
void printStats() { runAll<printStats>(); }
but this does not work (did not expect it to). The problem with passing function name as a function argument (which I see is many other questions such as here is that I do not know how to point to various ::update() functions from BaseSensor::update(). for example
void update() { runAll<update>( update() ); }
is also not correct.
Is it possible to avoid copying in this case? Can this be done in a one-liner so as to avoid alot of copying using c++11 (i.e. without using generic lambdas as is done here)? How would the template parameters look like if I where to move a working runAll() into file "sensor.t.hpp" ?
Thank you.

Answer 1

As long as the functions to be called are two, you can use a dedicated structure and rely on overloading to solve it.
It follows a minimal, working example:
#include<iostream>
struct Executor {
template<typename T>
static void execute(int, T &t) {
t.update();
}
template<typename T>
static void execute(char, T &t) {
t.printStats();
}
};
struct EdgeSensor
{
void update() { std::cout << "EdgeSensor::update" << std::endl; }
void printStats() { std::cout << "EdgeSensor::printStats" << std::endl; }
};
struct TrendSensor
{
void update() { std::cout << "TrendSensor::update" << std::endl; }
void printStats() { std::cout << "TrendSensor::printStats" << std::endl; }
};
template<typename ... SensorType>
class BaseSensor : public SensorType ...
{
template<typename T>
void execute() {
int arr[] = { (Executor::execute(T{}, static_cast<SensorType&>(*this)), 0)..., 0 };
(void)arr;
}
public:
void update() {
execute<int>();
}
void printStats() {
execute<char>();
}
};
int main() {
BaseSensor<EdgeSensor,TrendSensor> ets;
ets.update();
ets.printStats();
}
In case you have more than two functions to be called, I guess the choice trick applies well here.

Answer 2

You can still write the (simplified version of) generic lambda manually:
void update() {
execute([](auto &t) { t.update(); });
}
becomes so
void update() {
struct {
template <typename T>
void operator () (T& t) const { t.update(); }
} updater;
execute(updater);
}