Functions

Reusable code

A function allows you to store code under a name and then execute that code later.

A function always starts with the function keyword followed by the name with parentheses and then opening and closing curly braces around the code.

<?php

function hello_world() {
    echo "hello world\n";
}

To call the function, use the function name with parentheses.

hello_world();

You can set up values to be passed into a function. To do so, write variables in between the function parentheses. Each one should be separated by a comma.

function greet($firstname, $lastname) {
    echo "hello $firstname $lastname\n";
}

Then, you can pass in values when calling a function. In the greet function, 'John' is assigned to $firstname and 'Smith' is assigned to $lastname.

greet('John', 'Smith');

You can also return a value from a function. You can only return a single value from a function.

function capitalize($value) {
    return mb_strtoupper($value);
}

When calling a function, it will output the return value which you can load into a variable.

$animal = capitalize('dog');
echo "$animal\n";

You can also create nameless functions called closures. Closures can be stored in variables or passed into other functions.

$sum = function ($a, $b) {
    return $a + $b;
};

You can execute a closure by putting parentheses after the variable that contains the closure.

echo $sum(1, 2) . "\n";