Subclass Array or not?

Question

I have to model a 15-puzzle game board in Ruby. As a representation, I chose to use a multidimensional array (as a classic 2x2 matrix) with rows and columns.

My question is: is it better to subclass Array, in order to store all the relevant informations inside self or is it better to create a new class, and internally use an instance variable to keep track of the multidim array?

The API is meant to be the same in both cases, my question is about the implementation.

It is not clear what you mean by "store all the relevant informations [information] inside `self`". — sawa, Oct 13 '13 at 16:09
@AndrewMarshall I understand that, but how is the OP saying to store information inside the array instance? As its elements? That is definitely a code smell. — sawa, Oct 13 '13 at 16:14
In addition, it is not clear how a 2x2 matrix is relevant to a 15-puzzle. — sawa, Oct 13 '13 at 16:15

score 2 · Answer 1 · answered Oct 13 '13 at 16:08

2

Your class will not be an array, so don't subclass it. It might be implemented with an array, but it isn't one.

Subclassing would violate LSP (Liskov Substitution Principle).

answered Oct 13 '13 at 16:08

Sergio Tulentsev

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Really you know too many principals about OOP.. :) – Arup Rakshit Oct 13 '13 at 16:10
@Arup Rakshit, those patterns didn't came out of nowhere - it's accumulated knowledge of many professionals in our field. The more You know about design patterns, the better it's for You. – Edgars Jekabsons Oct 13 '13 at 16:15
@EdgarsJekabsons Yes..you are right...That's why I do appreciate..I am very new to OOP,and also started learning this OOP tech holding the hand of Ruby... – Arup Rakshit Oct 13 '13 at 16:18
@ArupRakshit See [SOLID](https://en.wikipedia.org/wiki/SOLID_(object-oriented_design)). – Andrew Marshall Oct 13 '13 at 17:12
That's what I wanted to hear :) Just a little thing: when you say "implemented with an array", what do you mean in Ruby? Having a private instance variable holding an array? – whatyouhide Oct 13 '13 at 18:24
@whatyouhide: yes, exactly that. It's called composition. – Sergio Tulentsev Oct 13 '13 at 18:25

score 0 · Answer 2 · answered Oct 13 '13 at 16:11

If You explore more on different OOD patterns, You will discover that one of the most common advices is to favour composition over inheritance. Inheritance might be fine for highly a hierarchical data structure. But in most cases You will just introduce extra dependencies.

Subclass Array or not?

2 Answers2