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Array of functions with different signatures

I have the following classes:

class Foo
{
    ...
};

class Foo1 : public Foo
{
    ...
};

...

class FooN : public Foo
{
    ...
};

Is it possible to have an array of functions with such signatures:

void f1(Foo1*){}
...
void fN(FooN*){}

Are there any changes if these functions are not static member functions instead of regular functions? I do not think that this will change anything.

Thank!

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10 answers

I found this workaround for this problem:

#include <iostream>
#include <vector>

class Foo
{
};

class Foo1 : public Foo
{
};

class Foo2 : public Foo
{
};

class Foo3 : public Foo
{
};


void f1(Foo1*)
{
    std::cout<<"f1\n";
}

void f2(Foo2*)
{
    std::cout<<"f2\n";
}

void f3(Foo3*)
{
    std::cout<<"f3\n";
}

template<typename T>
void AddPointer(std::vector<typename void (*)(Foo*)>& fPointers, T function)
{
    fPointers.push_back(reinterpret_cast<void (*)(Foo*)>(function));
}

void main()
{
    std::vector<typename void (*)(Foo*)> fPointers;

    AddPointer(fPointers, f1);
    AddPointer(fPointers, f2);
    AddPointer(fPointers, f3);

    Foo1 foo1;
    Foo2 foo2;
    Foo3 foo3;

    fPointers[0](&foo1);
    fPointers[1](&foo2);
    fPointers[2](&foo3);
}
0
source

EDIT an alternative solution based on non-virtual functions here .

A type void(*)(Foo*)cannot be converted to a type void(*)(Bar*)and not without reason.

Interface*, FooN Interface

struct Interface {
    virtual ~ Interface () {}
    // ...
};

struct Foo1 : public Interface {
    // ...
};

struct Foo2 : public Interface {
    // ...
};

void f1 (Interface *);
void f2 (Interface *);

void (*functions)(Interface*) [] = {f1, f2};

functions[0] (new Foo1 ());
functions[0] (new Foo2 ());
functions[1] (new Foo1 ());
functions[1] (new Foo2 ());

f1, f2 , dynamic_cast nullptr. - f1 f2 , .

- , , -,

+3

. . , . , boost.signal/boost.bind ++ 0x.

class Foo1 {};
class Foo2 {};
class Foo3 {};

void func1(Foo1*) {}
void func2(Foo2*) {}
void func3(Foo3*) {}

class FuncObjBase {
public:
    virtual void operator()() = 0;
};

template <class T>
class FuncObj : public FuncObjBase {
public:
    typedef void (*Funcptr)(T*);
    FuncObj(T* instance, Funcptr funcptr) : m_Instance(instance), m_Func(funcptr) {}
    virtual void operator()() { m_Func(m_Instance); }
private:
   T* m_Instance;
   Funcptr m_Func;
};

int main(int argc, char *argv[])
{
    Foo1 foo1;
    Foo2 foo2;
    Foo3 foo3;
    FuncObjBase* functions[3];
    functions[0] = new FuncObj<Foo1>(&foo1, func1);
    functions[1] = new FuncObj<Foo2>(&foo2, func2);
    functions[2] = new FuncObj<Foo3>(&foo3, func3);
    for(unsigned int i = 0; i < 3; i++) {
        (*functions[i])();
    }
    return 0;
}
+2

++ - . ++ , ( ) .

, , , . - , . . , , .

, , boost::variant. , , , boost::function. , . , , , .

boost::any. , . , . , . , , .

, boost::tuple "". , , . , , struct, .

+1

++ 11 Variadic. , , , : fooobar.com/questions/172571/...

+1

.

, Boost.Signal ++ 0x/TR1

0

f1 fN , . - .

0

. ++, . , :

struct Vehicle {};
struct Tricycle : Vehicle {};
struct Tank : Vehicle {};

void drive(Vehicle const & b) { ... }
void giveToChild(Tricycle const & b) { ... }

, , . , , , :

typedef void (*funcPtr)(Vehicle const &);

funcPtr = &giveToChild; // this is not allowed
funcPtr(Tank());        // oops, I just gave a tank to my child!

, , ++.

() - (, # ), , , ++. , :

typedef void (*funcPtr)(Tricycle const &);

funcPtr = &drive;    // this could be allowed, but is not (in C++)
funcPtr(Tricycle()); // I can only drive a tricycle, but that ok since it a
                     // vehicle and I know how to drive all vehicles

, , , , , :

void forwardFN(Foo * f)
{
    FooN * instance = dynamic_cast<FooN *>(f);

    if (instance) fN(instance);
    else throw type_exception();
}
0

std::tuple std::array C-. std::tuple, .

0

, .

class Manager {
public:

    typedef int /* or whatever */ ID;

    template <typename Function>
    static void save (Function * f, ID id) {
        functions <Function> () .add (id, f);
    }

    template <typename Function>
    static Function * get (ID id) {
        return functions <Function> () .get (id);
    }

private:

    template <typename Function>
    class FunctionStore {
    public:

         void add (Function *, ID);
         Function * get (ID);

    private:
         // or vector, if you know ID is int.
         std :: map <ID, Function *> m_functions;
    };

    // type_index is C++11 but you can implement it in C++03.
    // void* here is unpleasant but you can improve it, RAII it.
    typedef std :: map <std :: type_index, void *> Store;
    static Store m_store;

    template <typename Function>
    FunctionStore <Function> & functions () {
        FunctionStore <Function> * fs;

        Store :: iterator i = m_store .find (typeid Function);

        if (m_store .end () == i) {
            fs = new FunctionStore <Function> ();
            m_store [typeid Function] = fs;
        }
        else {
            // This void* cast is OK because it internally controlled
            // and provably correct.
            // We don't have to trust the library to not abuse it.
            fs = static_cast <FunctionStore<Function>*> (i -> second);
        }

        return *fs;
    }
};

// In the library

void foo1 (Foo *);
void bar1 (Bar *);
void foo2 (Foo *);
void bar2 (Bar *);

void init () {
    Manager :: save (foo1, 1);
    Manager :: save (foo2, 2);
    Manager :: save (bar1, 1);
    Manager :: save (bar2, 2);

    Manager :: get <void(Foo*)> (1) (new Foo ()); // OK, calls foo1
    Manager :: get <void(Foo*)> (1) (new Bar ()); // Will not compile
    Manager :: get <void(Bar*)> (2) (new Bar ()); // OK, calls bar2
}

m_store (/ void Manager::Store), Manager , - m_store. , , Function.

void init () {
    Manager <void(Foo*)> :: save (foo1, 1);
    Manager <void(Foo*)> :: save (foo2, 2);
    Manager <void(Foo*)> :: save (bar1, 1); // Won't compile
    Manager <void(Bar*)> :: save (bar1, 1);
    Manager <void(Bar*)> :: save (bar2, 2);

    Manager <void(Foo*)> :: get (1) (new Foo ()); // OK, calls foo1
    Manager <void(Foo*)> :: get (1) (new Bar ()); // Will not compile
    Manager <void(Bar*)> :: get (2) (new Bar ()); // OK, calls bar2
}

init , : , , , . , , .

0

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