Why do I have to declare __set if I declare __get for read-only properties?

[C Drozdowski <c.d@xxxxxxxxxxxxx>]

Howdy,

I'd like to access some of the private members of my classes as 
read-only properties without resorting to function calls to access 
them. (e.g. $testClass->privateMember instead of 
$testClass->privateMember(), etc)

Based on my research and testing, using the __get and __set overloading 
methods appears to be the only way to do so. It also, based on testing, 
appears that these private members must be in an array.

What I do not understand is that if I declare a __get method I MUST 
also declare a "do nothing" __set method to prevent the read-only 
properties from being modified in code that uses the class.

For example, the code below allows me to have read-only properties. 
However, if I remove the "do nothing" __set method completely, then the 
properties are no longer read-only.

I'm curious as to why I HAVE to implement the __set method?

Example:

<?php

class testClass
{
   private $varArray = array('one'=>'ONE', 'two'=>'TWO');

   public function __get($name)
   {
       if (array_key_exists($name, $this->varArray)) {
           return $this->varArray[$name];
       }
   }

   public function __set($name, $value)
   {
   }

}

$test = new testClass();

$test->one = 'TWO';   // doesn't work
echo $test->one;      // echo s 'ONE'

?>

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