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PHP PHP Functions Function Returns and More PHP Variable Functions

Jon Maldia
Jon Maldia
8,473 Points
Posted by Jon Maldia
Jon Maldia
8,473 Points

What is the practical use of using Variable Functions?

Is there any practical use for using variable functions? I guess using it for testing functions but is there any other reason why you would want to create a variable function?

3 Answers

Hugo Paz
Hugo Paz
15,622 Points
Hugo Paz
Hugo Paz
15,622 Points

You could use it for a callback function.

Basically you pass a function to a function.

From the php manual

<?php
// Our closure
$double = function($a) {
    return $a * 2;
};

// This is our range of numbers
$numbers = range(1, 5);

// Use the closure as a callback here to 
// double the size of each element in our 
// range
$new_numbers = array_map($double, $numbers);

print implode(' ', $new_numbers);
?>

The above example will output:

2 4 6 8 10

Jon Maldia
Jon Maldia
8,473 Points
Jon Maldia
Jon Maldia
8,473 Points

excellent! thanks so much hugo!

ammarkhan
.a{fill-rule:evenodd;}techdegree
ammarkhan
Front End Web Development Techdegree Student 21,661 Points

Hugo Paz Hi, can you give a easy example. This example crossed over my head.

Hugo Paz
Hugo Paz
15,622 Points
Hugo Paz
Hugo Paz
15,622 Points

Hi @ammarkhan,

Maybe this example will help

<?php
error_reporting(E_ALL);
ini_set("display_errors", 1);

$double = function($number){
    return $number * 2;
};

$numbers = [10, 20 , 30, 40, 50];

function doubleUp($func, $arr){

    $max = sizeof($arr);

    for($i = 0; $i < $max; $i++){

        echo $func($arr[$i]) . '<br/>';
    }
};

doubleUp($double, $numbers);


?>

So we create an anonymous function (closure) and assign it to the variable $double.

We then create an array with a few numbers.

We then create a function called doubleUp which takes as arguments a function ($func) and an array ($arr).

We then use them both to echo out the values on the screen.

kabir k
PLUS
kabir k
Courses Plus Student 18,036 Points
kabir k
kabir k
Courses Plus Student 18,036 Points

An important reason for creating variable functions is that they are very useful for callbacks.

And it helps to understand what variable functions are.

Using examples from the video, from the variable, $func, we can switch the function's name (as a string), from 'answer' 

<?php

function answer( ){
    return 42;
}

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

$func = 'answer';

 echo $func( ); // using echo to print the returned value of the answer function, 42 to the screen

to 'add_up'

<?php

function answer( ){
    return 42;
}

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

$func = 'add_up';

 echo $func(5, 10); // using echo to print the returned value of the add_up function, 15 to the screen

The variable involved in a variable function is like a canister or container holding our function except that it holds the function’s name as a string and can be switched out with another function to allow us to use the functionality of the new function i.e. the function’s name it is currently holding (without having to have to modify the first function and thus we can have multiple custom functions that do different things)

That is, the string variables allow us to call pre-existing functions based on the functions' names as their values

And this concept makes the functions, variable functions.

William Twiner
William Twiner
2,605 Points
William Twiner
William Twiner
2,605 Points

Whew still way over my head at this time of the course