Accessing variables shared between classes within an aggregator class

Question

I have a problem in hand which requires to make a very modular design for different algorithms. For example population based optimization algorithms like genetic algorithm, particle swarm algorithm etc. There are several variants of these algorithms, therefore I planned to make the smaller building blocks as an abstract class and let the specific building block to be plugged in.

For example lets say we have algo1 which can be divided in the following subroutines

algo1
loop
{
  sub1 ()
  sub2 ()
  sub3 ()
}

For this I can create three interfaces which the implementation will override as per their implementation. Therefore

//Sub1Class, Sub2Class, Sub3Class are interfaces/abstract classes
class algo1
{
  sub1Class *sub1Obj;
  sub2Class *sub2Obj;
  sub3Class *sub3Obj;
}

// constructor or setter method to set the implementation 
algo1 (Sub1Class *myAlgo1Obj, Sub2Class myAlgo1Obj, Sub3Class myAlgo1Obj)
{
  sub1Obj = myAlgo1Obj;
  sub2Obj = myAlgo2Obj;
  sub3Obj = myAlgo3Obj;
}

doAlgo1
{
  loop
  {
    sub1Obj->algo ();
    sub2Obj->algo ();
    sub3Obj->algo ();
  }
}

This can be done, but all the algorithms uses the attributes of the algo class and there are intermediate variables shared by the algorithms which I do not want to give a getter/setter.

My question is what are the techniques which can be used to manage the shared intermediate variables between the algorithms. I can pass it as the algo method implementation argument, but the number of intermediates and the types may change from one implementation to another. In that case will it be a good idea to create a separate class of temporary variable or make something like friend in cpp? Note that the intermediate results can be large vectors and matrices.

Please let me know if you need more information or clarification.

NOTE: I can possibly omit the variables shared between the algorithms by introducing locals and re-computation, but the algorithms are iterative and computation intensive involving large matrices therefore I want to make object creation and destruction as minimum as possible.

Answer 1

I can propose to use Inverse of Control container to solve your problem.

First you should create several abstract classes to keep it in the container:

class ISubroutineState {
public:
    ISubroutineState() = default;

    virtual int getVar1() const = 0;
    virtual void setVar1(int v1) = 0;
};

class ISubroutineState1 : public ISubroutineState {
public:

    virtual std::string getVar2() const = 0;
    virtual void setVar2(std::string& v2) = 0;
};

The example of the subroutine state class implementation:

class SubState1 : public ISubroutineState1 {
    int var1;
    std::string var2;

public:
    int getVar1() const {
        return var1;
    }

    std::string getVar2() const {
        return var2;
    }

    void setVar1(int v1) { var1 = v1; }
    void setVar2(std::string& v) { var2 = v; }  
};

The the IoC container (please note it can be accessed in any way allowed - i used just static pointer for simplicity):

class StateBroker
{
    std::map<const char*, ISubroutineState*> *storage;
public:
    StateBroker();

    template <class S>
    void StateBroker::bind(S* state) {
        storage->emplace(typeid(S).name(), state);
    }

    template <class S>
    S* StateBroker::get() const {
        auto found = storage->find(typeid(S).name());
        if (found == storage->end()) return NULL;
        return (S*)found->second;
    }

    ~StateBroker();
};

StateBroker* stateBroker;

Now you can implement any type of the subroutines:

 class ISubroutine {
 public:
    virtual void Execute() = 0; 
 };

class Sub1Class : public ISubroutine {
public:
    void Execute()
    {
        if (stateBroker == NULL)
        {
            std::cout << "Sub1 called" << std::endl;
        }
        else {
            ISubroutineState1* ss1 = stateBroker->get<ISubroutineState1>();
            std::cout << "Sub1 with state called" << std::endl;
            ss1->setVar1(1);
            ss1->setVar2(std::string("State is changed by Sub1Class"));
            std::cout << *static_cast<SubState1*>(ss1) << std::endl;
        }
    }
};

class Sub2Class : public ISubroutine {
public:
    void Execute()
    {
        if (stateBroker == NULL)
        {
            std::cout << "Sub2 called" << std::endl;
        }
        else {
            ISubroutineState* ss1 = stateBroker->get<ISubroutineState>();
            std::cout << "Sub2 with state called" << std::endl;
            ss1->setVar1(2);
            std::cout << *static_cast<SubState1*>(ss1) << std::endl;
        }
   }
};

class Sub3Class : public ISubroutine {
public:
    void Execute()
    {
        if (stateBroker == NULL)
        {
            std::cout << "Sub3 called" << std::endl;
        }
        else {
            ISubroutineState1* ss1 = stateBroker->get<ISubroutineState1>();
            std::cout << "Sub3 with state called" << std::endl;
            ss1->setVar1(3);
            ss1->setVar2(std::string("State is changed by Sub3Class"));
            std::cout << *static_cast<SubState1*>(ss1) << std::endl;
        }
    }
};

Also please note that subroutine' Execute() can request any type of subroutine state it requires to perform their tasks. It can even create additional state instances (to use in later stage of the algorithm, for example).

Now the main algorithm would look like this:

class Algo {
private:
    Sub1Class* sub1;
    Sub2Class* sub2;
    Sub3Class* sub3;

public:
    Algo(Sub1Class* s1, Sub2Class* s2, Sub3Class* s3) : sub1(s1), sub2(s2), sub3(s3){}

    void Execute()
    {
        sub1->Execute();
        sub2->Execute();
        sub3->Execute();
    }
 };

... and it's usage (please note it can be used as stateless and as statefull depending on the fact the StateBroker is initialized or not)

Sub1Class s1;
Sub2Class s2;
Sub3Class s3;
std::cout << "Stateless algorithm" << std::endl;
Algo mainAlgo(&s1, &s2, &s3);
mainAlgo.Execute();

stateBroker = new StateBroker();
SubState1* state = new SubState1();
stateBroker->bind<ISubroutineState>(state);
stateBroker->bind<ISubroutineState1>(state);

std::cout << "Statefull algorithm" << std::endl;
Algo statefulAlgo(&s1, &s2, &s3);
statefulAlgo.Execute();

Please note that Algo class doesn't know anything about subroutine states, state broker, etc.; Sub2Class doesn't know about ISubroutineState1; and StateBroker doesn't care about state and subroutine implementation.

BTW, you can review the example project at https://github.com/ohnefuenfter/cppRestudy (VS2015)