PHP is the language that allows the developer to be more specific about what functions are getting and returning. Also, we have seen the implementation of the user-defined functions in PHP in our previous post:
https://padhle.com/functions-in-php-user-defined/
We can—always optionally— specify the type of argument that the function needs (type hinting), and the type of
result the function will return (return type).
Let’s first see an example:
<?php
declare(strict_types=1);
function addNumbers(int $a, int $b, bool $printSum): int {
$sum = $a + $b;
if ($printSum) {
echo 'The sum is ' . $sum;
}
return $sum;
}
addNumbers(1, 2, true);
addNumbers(1, '2', true); // it fails when strict_types is 1
addNumbers(1, 'something', true); // it always fails
This preceding function states that the arguments need to be integer, integer, and Boolean, and that the result will be an integer.
Now, we know that PHP has type juggling, so it can usually transform a value of one type to its equivalent value of another type, for example, the string “2” can be used as integer 2.
To stop PHP from using type juggling with the arguments and results of functions, we can declare the directive strict_types as shown in the first highlighted line. This directive has to be declared at the top of each file where we want to enforce this behavior.
The three invocations work as follows:
• The first invocation sends two integers and a Boolean, which is what the function expects, so regardless of the value of strict_types, it will always work.
• The second invocation sends an integer, a string, and a Boolean. The string has a valid integer value, so if PHP was allowed to use type juggling, the invocation would resolve just normally. But in this example, it will fail because of the declaration at the top of the file.
• The third invocation will always fail as the string “something” cannot be transformed into a valid integer. Let’s try to use a function within our project.
In our index.php, we have a foreach loop that iterates the books and prints them. The code inside the loop is kind of hard to understand as it is a mix of HTML with PHP, and there is a conditional too.
Let’s try to abstract the logic inside the loop into a function.
First, create the new functions.php file with the following content:
<?php
function printableTitle(array $book): string {
$result = '<i>' . $book['title'] . '</i> - ' . $book['author'];
if (!$book['available']) {
$result .= ' <b>Not available</b>';
}
return $result;
}
This file will contain our functions. The first one, printableTitle, takes an array representing a book, and builds a string with a nice representation of the book in HTML.
The code is the same as before, just encapsulated in a function. Now index.php will have to include the functions.php file, and then use the function inside the loop.
Let’s see how:
<?php require_once 'functions.php' ?> <!DOCTYPE html> <html lang="en"> //... ?> <ul> <?php foreach ($books as $book): ?> <li><?php echo printableTitle($book); ?> </li> <?php endforeach; ?> </ul> //...
Well, now our loop looks way cleaner. Also, if we need to print the title of the book somewhere else, we can reuse the function instead of duplicating code.