Don't assign value to reference variable.

Objective:

        I just tried to create linked list in php. 

Challenges:

    In php array is sufficient for most data types (simple array, multi-dimensional array and key-value associative array). But, i just tried using stdClass Object (pre-defined interfaces and class). Here, I created one stdClass with reference key and it reference to another class up to final and that final class  reference key is null. Here I used reference key as reference variable. Once i started assigning reference value to this key it assigning new value to it and old one erased.

$a = new stdClass();
$a->name = "Trial";
$a->ref = null;
for($i=1;$i <= 10;$i++){
 $b = new stdClass();
 $b->name = 'Demo mj '.$i;
 $b->ref = null;
 if($a->ref === null ){
  $a->ref = &$b;
 }else{
  $current = $a->ref;
  while($current->ref !== null){
   $current = $current->ref;
  }
  $current->ref = &$b;
 }
}
print_r($a);
unset($current);
$current = $a->ref;
while($current->ref !== null){
 echo $current->name.PHP_EOL;
 $current = $current->ref;
}


When i run this code it gives below output. It assigned final stdClass to first stdClass reference key.

Technology:

    1. PHP 8.2

Variables in PHP;

    1. Super global variables

    2. Global variable

    3.Function variable

    4. Obscure variable names - ${'invalid-name'}

    5. Reference variable $a = &$b

    6. Variable variables - 

$a = "hello"; 

$hello = "world"; 

echo $a." ".$$a; 

 result = hello world 

Reference Variables:

    Here, problem came from reference variable. I thought reference variables are reference that variable but, it shares value commonly and if change any one variable value to change that variable value. So, Once i assign value to that reference variable it assigned new value to that shared value (or change original value).That's why I lost old values. This technic is useful when we want to change original value within function scope.

    Now changed that code and just record it in github repository. https://github.com/Aathiappan/LearningPHP/blob/main/DataStructure/LinkedList.php

Conclusion:

    PHP reference variable not store variable memory address it shares value. It's also useful in function scope. 

    Ref: https://www.php.net/manual/en/language.references.arent.php