Question

I think this is a really newb question, but I never found out the answer. I don’t know how exactly to phrase this question, but I often find that I have to access objects that are “far away” from the current object in terms of the current hierarchy. I just want to make sure that this is the right (only) way to do this.

This goes along with passing parameters in from main also. I find that some objects far away from main need to be passed in with a parameter multiple times. How does an object far away from main get information from the command line?

For example for the first case, for 4 classes…

class A{
   B b;
   //need to check status of D

   //choice 1
   b.get_c().get_d().get_status();  

   //choice 2
   const C& c = b.get_c();
   const D& d = c.get_d();
   d.get_status();
};

class B{
public:
   C c;
   const C& get_c() {return c;}
};

class C{
public:
   D d;
   const D& get_d() {return d;}
};

class D{
public:
   bool check_status();
};

Say something like, A is car, B is door assembly, C is door, D is lock. Then A has to check say, is lock on, otherwise prevent starting.

Choice 3 is to directly call D’s method from A, I’d have to make a few layers of check_status() in C, B, and A and return D, C, B.check_status().

Don’t all these calls to subobjects (if the code was a bit more complicated) get a lot of overhead?

Thanks.

Answer 1

The answer to this sort of question is always the same: Don’t worry about it unless and until it becomes a problem, and then, take measurements to decide which option is best. Yes, there’s an overhead with calls to subobjects but with the example you’ve given (and with many real-life examples) this overhead is unavoidable (and the compiler may optimize some of it away anyway).