lambda-expressions-and-closures.md

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Lambda Expressions and Closures

How do lambda expressions work?

PHP

PHP allows for the assignment of anonymous inner functions to variables. The keyword for their creation is still function, identical to standard named function creation.

<?php
    $celciusToFarenheight = function($t) { return (9/5)*t+32; };
    print $celciusToFarenheight(13);
?>

Will yield 55.4.

Python

Python allows lambda expressions as small anonymous (unnamed) functions. These are defined with the lambda keyword, and can consist of only a single expression.

celciusToFarenheight = lambda t: (float(9)/5)*t+32
print(celciusToFarenheight(13))

Will yield 55.400000000000006.

How do closures expressions work?

PHP

PHP can access variables outside of its own scope with the use keyword.

<?php
    $padding = 30;
    $width = function($w) use ($padding) { return $w+($padding*2); };
    print($width(100));
?>

Will yield 160.

Python

Python can remember values in an enclosed scope even if the values are not present in memory. This can avoid use of global variables and allow for neater code. The following example was borrowed from this documentation and provides an example of closure in Python:

def multiplier_of(n):
    def multiplier(number):
        return number*n
    return multiplier

multiplywith5 = multiplier_of(5)
print(multiplywith5(9))

Will yield 45.