Closures, Anonymous Function & High Order Functions in PHP

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Closures are introduced in PHP 5.3. Functions which are created without any name (Anonymous Function) and Closures functions are used to represent these kind of functions.

A closure is good when we want a local function that’s only used for some small specific purposes.

Basically, Closure are the inner functions that have access to outer variables and used as a callback function to anonymous functions.

Simple Php Closure example

High Order function are related to functional programming. Basically these kind of functions has at least one of these features.

• Takes one or more functions as arguments.
• Return a function as its result.

Simple High Order Function example

Here are some inbuilt High Order Functions in PHP which will be more helpful to write clean and fast codes.

• array_map
• array_filter
• array_reduce
• array_walk

array_map : Applies the callback to the elements of the given arrays

array_filter : Filters elements of an array using a callback function

array_reduce: Iteratively reduce the array to a single value using a callback function

array_walk : Apply a user supplied function to every member of an array

PS; One more thing. lets try to use external variable inside high order function here : array_map

$add = 2;
$lists = [1,2,3,4,5];
array_map(function($value){
 return $value + $add;
 }, $lists);

We will get this error: Undefined variable: add

To solve this, we need to supply external variable to function using `use` keyboard.