Lazy construction is a virtual method against if-then to drown out the getter

Question

The background of my problem is that I'm trying to create a lazy grid structure where grid areas are created only when necessary, otherwise they return the default value when prompted.

Having unwrapped the problem a bit, consider the following layout of my situation:

struct Container {
  std::vector<Base> data;

  float get(int indexOuter, int indexInner) {
     return data[indexOuter].get(indexInner);
  }
}

I want to stub the function Base::getin some cases, to always return the same value, while in other cases I want to return the value to some array. I present two possible solutions.

The first solution is to use a flag Base, i.e.

struct Base {
  std::vector<float> data;

  float get(int indexInner) {
    if (data.empty()) return 0;
    return data[indexInner];
  }
}

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struct Container {
  std::vector<Base*> data;

  float get(int indexOuter, int indexInner) {
     return data[indexOuter]->get(indexInner);
  }
}
struct Base {
  virtual float get(int indexInner) = 0;
}
struct Stub : public Base {
  float get(int indexInner) {
    return 0;
  }   
}
struct Concrete : public Base {
  std::vector<float> data;

  float get(int indexInner) {
    return data[indexInner];
  }   
}

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Answer 1

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