Optimization Through Built-in Functions in PHP

Suppose a programmer checks if the array contains the number 5:

<?php
	$arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
	
	$exists = false;
	foreach ($arr as $elem) {
		if ($elem == 5) {
			$exists = true;
			break; // exit the loop to avoid unnecessary iterations
		}
	}
	
	var_dump($exists);
?>

I claim that there is something wrong with this code. What is it? We exit the loop after finding the number 3, right? The fact is, that built-in PHP functions always work an order of magnitude faster than similar custom code.

In our case, there is a function in_array that solves the given task - and we should use exactly this function:

<?php
	$arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
	var_dump(in_array(3, $arr));
?>

Moral: before solving a task, always check if there is a built-in PHP function for its solution.

In the following code, a programmer finds the sum of array elements. Optimize this programmer's solution.

Here is the code:

<?php
	$arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
	
	$sum = 0;
	foreach ($arr as $elem) {
		$sum += $elem;
	}
	echo $sum;
?>

In the following code, a programmer finds the product of array elements. Optimize this programmer's solution:

<?php
	$arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
	
	$res = 1;
	foreach ($arr as $elem) {
		$res *= $elem;
	}
	echo $res;
?>