Tag Archives: Closure

Closures

Anonymous functions, implemented in PHP 5.3, yield objects of this type. This fact used to be considered an implementation detail, but it can now be relied upon. Starting with PHP 5.4, this class has methods that allow further control of the anonymous function after it has been created.

• Enable creation of functions without specifying a name

• Implemented using the closure class

• Commonly used as param value for callback functions, or alternatively as variable values

• To inherit variables from parent scope (function in which closure was declared), these variables must be declared in the function header with the “USE” keyword, or passing parameters in the call line

• new closure TYPE HINT

bindTo

Closure::bindTo — Duplicates the closure with a new bound object and class scope

Create and return a new anonymous function with the same body and bound variables as this one, but possibly with a different bound object and a new class scope.

The “bound object” determines the value $this will have in the function body and the “class scope” represents a class which determines which private and protected members the anonymous function will be able to access. Namely, the members that will be visible are the same as if the anonymous function were a method of the class given as value of the newscope parameter.

Static closures cannot have any bound object (the value of the parameter newthis should be NULL), but this function can nevertheless be used to change their class scope.

This function will ensure that for a non-static closure, having a bound instance will imply being scoped and vice-versa. To this end, non-static closures that are given a scope but a NULL instance are made static and non-static non-scoped closures that are given a non-null instance are scoped to an unspecified class.

Closure

A Closure is essentially the same as a Lambda apart from it can access variables outside the scope that it was created.

For example:
<?php
 $user = "PHPCodez";
 // Create a Closure 
 $greeting = function() use ($user) { 
 echo "Hello $user"; 
 };

$greeting();

As you can see above, the Closure is able to access the $user variable. because it was declared in the use clause of the Closure function definition.

If you were to alter the $user variable within the Closure, it would not effect the original variable. To update the original variable, we can append an ampersand. An ampersand before a variable means this is a reference and so the original variable is also updated.

Closures are also useful when using PHP functions that accept a callback function like array_map, array_filter, array_reduce or array_walk.

The array_walk function takes an array and runs it through the callback function.

Again, you can access variables outside the scope of the Closure by using the use clause:

In the example above, it probably wouldn’t make sense to create a function to just multiply two numbers together. If you were to create function to do a job like this, then come back to the code a while later you will probably be thinking why did you bother create a globally accessible function only to be used once? By using a Closure as the callback, we can use the function once and then forget about it.