Functions

Functions do things, they are the verbs of programming. By using functions in our code we improve:

• Modularity, by allowing us to break down a larger program into smaller parts.
• Reusability, by allowing us to reuse code without having to retype or copy/paste it.
• Readability, by allowing us to give descriptive names to specific parts of our program.

Table of Contents

1. Functions
2. Scope
3. Type Declarations
4. Return Type Declarations
5. Allowed Types and Type Errors

Functions

PHP functions can be defined to take zero of more parameters and can return any type of variable.

<?php
    function square($x) {
        return $x * $x;
    }
    echo "16 squared = " . square(16);
?>

If your function has nothing to return you need not use the return keyword. A function will automatically return when there are no more statements to execute.

<?php

function say_good_day($name) {
    echo "A fine day indeed {$name}!";
}

say_good_day('Bobby McGee');

?>

Scope

All variables in PHP (created outside of functions) exist in a global scope. Function have a separate local scope. Variables used inside a function leave scope when the function exits.

<?php
    $magic_words = 'abracadabra';
    function scope_scoop() {
        echo "Inside Function 1: {$magic_words}\n";
        $magic_words = 'Bibbidi-bobbidi-boo';
        echo "Inside Function 2: {$magic_words}\n" ;
    }
    scope_scoop();
    echo "Outside Function : {$magic_words}" ;
?>

Output:

Notice:  Undefined variable: magic_words in C:\xampp\htdocs\php\text.php on line 4
Inside Function 1:
Inside Function 2: Bibbidi-bobbidi-boo
Outside Function : abracadabra

Scope defines where in a program a variable is accessible. Where ever a variable is not accessible by your program it is said to be “out of scope” or “outside the current scope.”

Resources

• Variable Scope @ PHP.net

Type Declarations

Earlier we learned that PHP variables were dynamically typed based on context. PHP 7 now allows programmers to apply strict typing to function parameters and return types.

Type declaration (also called type hinting) is optional but it can make your functions less error prone.

Here’s an example of a function that will only accept an integer as its only argument:

function hello_n_times( int $count ) {
    for ($i = 0; $i <= $count; $i++) {
        echo "Hello";
    }
}

Return Type Declarations

With type declarations we can also specify the return type of a a function.

Here’s a function that accepts two floats and returns a string:

    function receipt_total(float $total, float $taxes) : string {
        $grand_total = $total + $taxes;
        return "Grand total after taxes: \${$grand_total}.";
    }

Allowed Types and Type Errors

Here are some of the main types that can be used as declarations:

PHP will throw a TypeError if the incorrect type of data is used in place of the declared type.

Resources

• Type Declarations @ PHP.net