Question

I am working on a C++ project, specifically implementing a shunting yard algorithm.

I have a function that creates a vector of shared_ptr‘s of type super class, but the classes that are being pushed into this vector are all base class shared_ptrs.

I then need to take this vector and pass it into another function and carry out different logic for each element of the vector in a for loop. The logic that I carry out, however, depends on which base class is present in each element of the vector.

So basically what I don’t know is how to identify which type of base class is in each element of the vector. When I debug they are all coming out as type super-class.

So generally I’d like to do something like this:

if(vectorElement == baseClass)
{
  //do some logic
}

Or if there is some different method of carrying this out which I’m missing I’d be interested in carrying that out.

Answer 1

There are many solutions to your problem, frankly is the almost most common problem in OOP.

The most obvious is the virtual function doing different things in different classes:

class SuperClass {
public:
   virtual void doSomething(/*someArgsIfNeeded*/) {
      // some base implementation, possible empty
      // or just use pure virtual function here
   }
};

class SubClass : public SuperClass {
public:
   virtual void doSomething(/*someArgsIfNeeded*/) {
      // some base implementation
   }
};

Then use it as follows:

int SomeArgs;
std::vector<std::shared_ptr<SuperClass>> objects;
for (auto it = objects.begin(); it != objects.end(); ++i)
  it->doSomething(/*someArgsIfNeeded*/);

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Other more sophisticated solution is to use visitor pattern.

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It is considered a bad practice to use casting (dynamic_cast), so always search for more OO solutions than casting, like these two I presented above.