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immutable.php

<?php

require_once __DIR__.'/MyObject.php';


$time = microtime(true);
$memory = memory_get_usage();

$object = new MyObject();
for ($i = 0; $i < 1000000; $i++) {
    $object = $object->setImmutableValue('value ' . $i);
}

$memory = memory_get_usage() - $memory;
$time = microtime(true) - $time;

echo "Memory usage: " . $memory . "<br/>";
echo "Time usage: " . $time . "<br/>";

mutable.php

<?php

require_once __DIR__.'/MyObject.php';

$time = microtime(true);
$memory = memory_get_usage();

$object = new MyObject();
for ($i = 0; $i < 1000000; $i++) {
    $object->setValue('value ' . $i);
}

$memory = memory_get_usage() - $memory;
$time = microtime(true) - $time;

echo "Memory usage: " . $memory . "<br/>";
echo "Time usage: " . $time . "<br/>";

MyObject.php

<?php
class MyObject
{
    private string $value;

    /**
     * @return string
     */
    public function getValue(): string
    {
        return $this->value;
    }

    /**
     * @param string $value
     */
    public function setImmutableValue(string $value): self
    {
        $obj = clone $this;
        $obj->value = $value;
        return $obj;
    }

    /**
     * @param string $value
     */
    public function setValue(string $value): void
    {
        $this->value = $value;
    }


}