Discussione Modello template funzione membro membro C++

Question

Provo a chiamare una funzione membro di un oggetto utilizzando una discussione.

Se la funzione non ha un modello variadic (Args ... args), nessun problema, funziona:

considerare i due classi:

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 */ 
    }; 
} 

Con questo, è OK.

---

Ora, aggiungere un modello variadic alle stesse funzioni:

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 ... */ 
    }; 
} 

Con questo codice, GCC non può essere compilato: (mi dispiace per questo messaggio di errore)

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 

Realmente non capisco perché questa differenza fa questo errore. E non posso aggiustarlo.

---

In entrambi i main.cpp è così:

/* 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); 

---

io uso: «versione di gcc 4.7.2 (Ubuntu/Linaro 4.7.2-2ubuntu1)»

---

ho provato:

std::thread(&GeneticThread<T>::func<Args...>, islands[0], f, size_enf, args ...); 

Ora ho un altro errore:

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

Prova:

std::thread(&GeneticThread<T>::func<Args...>, islands... 

func è ora una funzione template. Devi specificare i suoi parametri del modello per essere in grado di prendere il suo indirizzo.