How do I Destroy a Static Variable in PHP? - php

Question

The answers to this question say that unset() doesn't work, but weren't clear on what does. I have a recursive function, which uses static variables, however after the recursion has finished and the value has been returned, I need to reset those variables or subsequent calls (the recursive function is currently been called within a loop) would return wrong values.
In the linked question some people suggested trying $var = NULL outside the function which I did, but to seemingly no effect.
The reason why I used static variables and didn't just write them as parameters to the function is that I don't want a situation where the user can pass in arguments to that function, as the only arguments to the function should be supplied from within it.
My Code
<?
require_once("randX.php"); #"randX()" generates a random floating point number in a specified range.
// require_once("../displayArray.php");
error_reporting(E_ERROR | E_WARNING | E_PARSE);
/*
* Generates a valid, random probability distribution for a given array of elements, that can be used in conjunction with "probSelect()".
* Input:
$arr: An array of elements.
$control: A value that decides how much mass is allowed to be unilaterally dumped onto one element. A high value would permit distributions where most of the mass is concentrated on one element.
If an invalid value is provided, the default is used.
* Output: An associative array where the keys are the elements in the original array, and the values are their probabilities.
* #param array $arr: An array of elements for which the probability distribution would be generated.
* #param float $control: A variable which limits the inequality of the probability distribution.
*/
function probGen(array $arr, float $control = 0.01)
{
$control = ($control <= 1 && $control >= 0)?($control):(0.00001); #Use the default value if an invalid number is supplied.
static $result = []; #Initialises $result with an empty array on first function call.
static $max = 1; #Initialises $max with 1 on first function call.
foreach ($arr as $value)
{
$x = randX(0, $max); #Random probability value.
$result[$value] = ($result[$value] + $x)??0; #Initialise the array with 0 on first call, and on subsequent calls increment by $x to assign probability mass.
$max -= $x; #Ensures that the probability never sums to more than one.
}
/*
* After the execution of the above code, there would be some leftover probability mass.
* The code below adds it to a random element.
*/
$var = array_values($arr);
if($max <= $control) #To limit concentration of most of the probability mass in one variable.
{
$result[$var[rand(0,(count($var)-1))]] += $max; #Selects a random key and adds $max to it.
// print("<br>Sum: ".array_sum($result)."<br>");
return $result;
}
else
{
return probGen($arr, $control);
}
}
$max = NULL;
unset($max);
$result = NULL;
unset($result);
?>

Answer 1

This is always the problem with using static in any circumstances, I would change them to be parameters being passed in and having a default value...
function probGen(array $arr, float $control = 0.01, $result = [], $max = 1 )
(With the appropriate types).
These can then be passed down the chain in your further call...
return probGen($arr, $control, $result, $max);
This allows you better control over what these values start as (you can pass in your own values as a default) as well as being able to reset/adjust them as part of the call.