Implementing sets using a PHP array

A set is a simply a collection of values without any particular order. It can contain any data type and we can run different set operations such as union, intersection, complement, and so on. As a set only contains values, we can construct a basic PHP array and assign values to it so that it grows dynamically. The following example shows two sets that we have defined; one contains some odd numbers and the other one has some prime numbers:

$odd = []; 
$odd[] = 1; 
$odd[] = 3; 
$odd[] = 5; 
$odd[] = 7; 
$odd[] = 9; 

$prime = []; 
$prime[] = 2; 
$prime[] = 3; 
$prime[] = 5; 

In order to check the existence of a value inside the set along with union, intersection, and complement operation, we can use the following example:

if (in_array(2, $prime)) { 
    echo "2 is a prime"; 
} 

$union = array_merge($prime, $odd); 
$intersection = array_intersect($prime, $odd); 
$compliment = array_diff($prime, $odd);  

PHP has many built-in functions for such operations and...