What advantage will Composite pattern bring me over just Array?

Answer 1

the value of composite is that you trade some complexity for being able to not break encapsulation.

In your array version you are breaking encapsulation since you are testing if the node is not a leaf:

if(isset($node['children'])) $this->print($node['children']);

with composite you can say:

print();

then run-time polymorphism will call the right method. In this case (I'm not a PHP programmer so let me to use a Java-like syntax):

class Node {

   void print() {
       for (child in children) {
          child.print();
       } 
   }

   ...
}

class Leaf {

   void print() {
       // print it! 
   }
}

another advantage over plain array is that you are hiding your implementation details (data structure, etc)

Answer 2

The point of the composite pattern is to be able to treat a collection of objects as if it were a single object (e.g. for displaying it or writing it to a file). As you write yourself "print() method may follow Iterator pattern later" - well, the point of the composite pattern would be that you could call print() without having to worry about whether you're printing a single Component or have to iterate through an entire Tree.

But it looks as though you're unclear about object-oriented programming in general, since you're considering using nested arrays instead. The value of using objects instead of hashes (which PHP arrays are) for everything is type safety, which makes it much easier to debug and maintain programs.

Answer 3

Doesn't the array implementation look a lot more complex to you? If I'm looking at it, I have to study it closer to understand what you're doing. You're dealing with indexes, assigning entries to specific indexes etc...it looks really complex.

Your implementation of the composite pattern on the other site looks simple and natural when you're looking at the code where you're using it. You have a node, and you attach other nodes or leafs to it. Nothing complex, strange, I don't have to care/remember indexes etc...That's why the composite pattern is useful in your case. Of course, its implementation may look a bit complex to you, if you're not accustomed to it, but the important point (as also other stated) is that you're hiding details. This is very important. It a simple example it may still work with your arrays, but when you implement such code in a production environment where possibly also other developers are editing/maintaining your code. If someone has to modify your "array" solution, it is much more probable that he'll introduce new bugs.

Answer 4

can u post the code for Tree structure implementation in java using composite design pattern.