Why declare variables?

Foo

I dont quite understand the point of declaring variables at the top of a class. Surely if you use a variable somewhere else in the class, it's automatically created for you?

The only thing I came up with was that perhaps it's related to the scope of a variable, but since there's that special 'global' keyword anyway, I'm still confused.


<?php
class Cart {
   var $items;  // Items in our shopping cart

   // Add $num articles of $artnr to the cart

   function add_item($artnr, $num) {
       $this->items[$artnr] += $num;
   }

   // Take $num articles of $artnr out of the cart

   function remove_item($artnr, $num) {
       if ($this->items[$artnr] > $num) {
           $this->items[$artnr] -= $num;
           return true;
       } else {
           return false;
       } 
   }
}
?>

Why not just this?


<?php
class Cart {

   // Add $num articles of $artnr to the cart

   function add_item($artnr, $num) {
       $this->items[$artnr] += $num;
   }

   // Take $num articles of $artnr out of the cart

   function remove_item($artnr, $num) {
       if ($this->items[$artnr] > $num) {
           $this->items[$artnr] -= $num;
           return true;
       } else {
           return false;
       } 
   }
}
?>

drew010

the thing about classes is that they are in most cases long and complex pieces of code and if you have variables in different functions you (and especially other programmers) wont have any what purpose they serve (local to the function, or used throughout the whole class). declaring all the important ones helps you keep track of things you have already handled or things you need to start keeping track of, not to mention if you have 50 class data members, you can look back and have a reference of everything, esp to other programmers who wish to use the class and access the class data members.

in php variable declaration in any case is not required, but in other languages, c++ especially, your program wont even compile if you use a variable that isnt declared.

Foo

Thanks. It's reassuring to know that they serve no 'true' function within the code. It feels better to be using them when you know precisely why you're doing so 😃

ahundiak

var is nice for initialization.

Add a method to cart

function getItems() { return $this->items; }
...
Then later:
$items = $cart->getItems();
foreach($items as $item) {
}

What happens if getItems is called before anything has been added? These types of errors can be difficult to avoid.
Using:
var $items = array();
Can save many headaches later.