Thread: OO confuses me

This isn't strictly C#, but since that's what I'm using , I'll post it here. OO-ing stuff confuses me.

I have a thing, it's say a location.

Code:

class Location
{
    ... coords;
}

Now, I actually want a whole pile of locations, say a grid:

Code:

class Grid
{
    ... dimensions
    Location[,] gridinfo;
}

Now I want different things to use my grid. I want actually the same grid to be used in different ways. I want something to show my grid, but not be able to mutate it. I also want something to mutate my grid, but not show it. So I make two more classes?

Code:

class GridPainter
{
}
class GridMutator
{
}

Now I could inherit a Grid:

Code:

class GridPainter : Grid
{
}

Or I could make its own private grid as a member of it, and write like a copy constructor, taking a Grid as an argument to the initializer:

Code:

class GridMutator
{
    Grid mutate;
    GridMutator( Grid toMutate ) { mutate = toMutate; }
}

(Except that's not actually a copy constructor, and it wouldn't even be worth using one here, since on the mutator I actually do want to mangle what I'm being passed, not just a copy of it).

I don't understand how to decide what is best. OO has always confused me, because I'm used to straight up C. I kinda get the is-a / has-a thing, but I'm still hung up on this. I'm not even sure there isn't another better way to do either of these.

See the Mutator has-a grid, actually it should be that it receives-a grid - or can I inherit a grid and have it be operating on the original? Ok, I make a base instance:

Code:

Grid mine = new Grid( 100, 100 );

Now I want to make a Mutator that works off of this one. Does this work? Does it even make sense?

Code:

GridMutator mut = new GridMutator( mine );

Is that even right? I don't get the inheritance thing. I mean I see how you can do it, if you just make a new instance, but what if I want to use an existing one? Do you not use inheritance there?

I'm too old to learn new tricks I think.


Quzah.