CODEWITHSUNDEEP
c++data-structures
user2381422
user2381422

Reputation: 5805

Data structures for objects positions, different objects can be indexed by different number of indices

I have structures to describe position for various objects in my project. Some objects are indexed by two, or three, etc. indices.

In this simple example I show 3 types of position A, B and C and they all inherit from Position which is empty. I inherit from Position so that I can pass these positions in functions that take Position argument. The reason why I don't use a single Position structure is that I would have to put all the members int a,b,c,d in it, and for some objects most of the time I will just use a and b for example:

struct Position {
};

struct A : public Position {
    int a,b,c,d;
};

struct B : public Position {
    int a,b,c;
};

struct C : public Position {
    int a,b;
};

The problem is, I have functions like this:

City &getCity(const Position &p) {
  const B &pos = (const B &)p;
  return rawSheets[pos.a].countries[pos.b].cities[pos.c];
}

Everything will be OK if I pass position of type B to this function, but what if I pass type A? And I need to do that.

Upvotes: 1

Views: 83

Answers (1)

Joe Z
Joe Z

Reputation: 17936

It seems like you actually want a hierarchy of position types, each more specific than the previous, somewhat like this:

struct Position1 
{
    int a;
};

struct Position2 : public Position1
{
    int b;
};

struct Position3 : public Position2
{
    int c;
};

struct Position4 : public Position3
{
    int d;
};

That way, you can use a Position4 wherever a Position1, Position2 or Position3 is needed, and the code will ignore the extra dimensions.

Upvotes: 1

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