Array References in PHP

In PHP, unlike other programming languages, arrays are also copied, not passed by reference.

Let's verify this:

<?php
	$arr1 = [1, 2, 3, 4, 5];
	$arr2 = $arr1;
	$arr2[0] = '!';
	
	var_dump($arr1); // won't change
?>

Now let's force the array to be passed by reference:

<?php
	$arr1 = [1, 2, 3, 4, 5];
	$arr2 = &$arr1;
	$arr2[0] = '!';
	
	var_dump($arr1); // will change
?>

Explain what the result of executing the code will be:

<?php
	$arr1 = [1, 2, 3, 4, 5];
	
	$arr2 = $arr1;
	$arr2[0] = '!';
	
	echo $arr1[0];
	echo $arr2[0];
?>

Explain what the result of executing the code will be:

<?php
	$arr1 = [1, 2, 3, 4, 5];
	
	$arr2 = &$arr1;
	$arr1[0]++;
	
	echo $arr1[0];
	echo $arr2[0];
?>

Explain what the result of executing the code will be:

<?php
	$arr1 = [1, 2, 3, 4, 5];
	
	$arr2 = &$arr1;
	
	$arr1[0]++;
	$arr2[0]++;
	
	echo $arr1[0];
	echo $arr2[0];
?>