Thread C++ member function template variadic template - c++

Question

I try to call a member function of an object using a thread.
If the function doesn't have a variadic template (Args ... args), no problem, it works:
Consider the two classes:
GeneticEngine
template <class T>
class GeneticEngine
{
template <typename ... Args>
T* run_while(bool (*f)(const T&),const int size_enf,Args& ... args)
{
std::thread(&GeneticThread<T>::func,islands[0],f,size_enf);
/* Some code */
return /* ... */
}
private:
GeneticThread<T>** islands;
}
GeneticThread
template <class T>
class GeneticThread
{
void func(bool (*f)(const T&),const int size_enf)
{
/* Some code */
};
}
With this, it's OK.
Now, I add a variadic template to the same functions:
GeneticEngine
template <class T>
class GeneticEngine
{
template <typename ... Args>
T* run_while(bool (*f)(const T&,Args& ...),const int size_enf,Args& ... args)
{
std::thread(&GeneticThread<T>::func,islands[0],f,size_enf,args ...);
/* Other code ... */
}
private:
GeneticThread<T>** islands;
}
GeneticThread
template <class T>
class GeneticThread
{
template <typename ... Args>
void func(bool (*f)(const T&,Args& ...), const int size_enf, Args& ... args)
{
/* Code ... */
};
}
With this code, GCC doesn't compile: (sorry for this error message)
g++ main.cpp GeneticEngine.hpp GeneticThread.hpp Individu.hpp GeneticThread.o -g -std=c++0x -o main.exe
In file included from main.cpp:2:0:
GeneticEngine.hpp: In instantiation of ‘T* GeneticEngine<T>::run_while(bool (*)(const T&, Args& ...), int, Args& ...) [with Args = {}; T = Individu]’:
main.cpp:24:78: required from here
GeneticEngine.hpp:20:13: erreur: no matching function for call to ‘std::thread::thread(<unresolved overloaded function type>, GeneticThread<Individu>*&, bool (*&)(const Individu&), const int&)’
GeneticEngine.hpp:20:13: note: candidates are:
In file included from GeneticThread.hpp:14:0,
from GeneticEngine.hpp:4,
from main.cpp:2:
/usr/include/c++/4.7/thread:131:7: note: template<class _Callable, class ... _Args> std::thread::thread(_Callable&&, _Args&& ...)
/usr/include/c++/4.7/thread:131:7: note: template argument deduction/substitution failed:
In file included from main.cpp:2:0:
GeneticEngine.hpp:20:13: note: couldn't deduce template parameter ‘_Callable’
In file included from GeneticThread.hpp:14:0,
from GeneticEngine.hpp:4,
from main.cpp:2:
/usr/include/c++/4.7/thread:126:5: note: std::thread::thread(std::thread&&)
/usr/include/c++/4.7/thread:126:5: note: candidate expects 1 argument, 4 provided
/usr/include/c++/4.7/thread:122:5: note: std::thread::thread()
/usr/include/c++/4.7/thread:122:5: note: candidate expects 0 arguments, 4 provided
I really do not understand why this difference makes this error. And I can not fix it.
In both the main.cpp is like that:
/* Individu is another class */
int pop_size = 1000;
int pop_child = pop_size*0.75;
GeneticEngine<Individu> engine(/*args to constructor*/);
bool (*stop)(const Individu&) = [](const Individu& best){
return false;
};
Individu* best = engine.run_while(stop,pop_child);
I use : «gcc version 4.7.2 (Ubuntu/Linaro 4.7.2-2ubuntu1) »
I tried:
std::thread(&GeneticThread<T>::func<Args...>, islands[0], f, size_enf, args ...);
Now I have another error:
GeneticEngine.hpp: In member function ‘T* GeneticEngine<T>::run_while(bool (*)(const T&, Args& ...), int, Args& ...)’:
GeneticEngine.hpp:20:53: erreur: expansion pattern ‘((& GeneticThread<T>::func) < <expression error>)’ contains no argument packs
GeneticEngine.hpp:20:24: erreur: expected primary-expression before ‘(’ token
GeneticEngine.hpp:20:53: erreur: expected primary-expression before ‘...’ token
template <typename ... Args>
T* run_while(bool (*f)(const T&,Args& ...), const int size_enf, Args& ... args)
{
void (GeneticThread<T>::*ptm)(bool (*)(T const&, Args&...), int, Args&...) = &GeneticThread<T>::func;
std::thread(ptm, islands[0], f, size_enf, args ...);
}

Answer 1

Try:
std::thread(&GeneticThread<T>::func<Args...>, islands...
func is now a template function. You have to specify its template parameters to be able to take its address.