Detailed explanation and example code of PHP closures

Closures and anonymous functions were introduced in PHP5.3.0.

A closure refers to a function that encapsulates the surrounding state when created. Even if the environment in which the closure is located no longer exists, the state encapsulated in the closure still exists.

Theoretically, closures and anonymous functions are different concepts. But PHP treats it as the same concept.

Actually, closures and anonymous functions are objects disguised as functions. They are instances of the Closure class.

Closures, like strings and integers, are first-class value types.

Create closure

<?php
$clousre = function ($name) {
return &#39;Hello &#39; . $name;
};
echo $closure(&#39;nesfo&#39;);

The reason why we can call the $closure variable is because the value of this variable is a closure, and the closure object implements the __invoke() magic method. As long as there is () after the variable name, PHP will find and call the __invoke() method. PHP closures are usually used as callbacks of functions. The array_map() and preg_replace_callback() methods all use callback functions. This is the best time to use closures!

For example:

<?php
$numbersPlusOne = array_map(function ($number) {
return $number + 1;
}, [1, 2, 3]);
print_r($numbersPlusOne);

Get the result:

[2, 3, 4]

Before the advent of closures, you could only create named functions individually and then reference that function by name. By doing this, the code execution will be slightly slower, and the implementation of the callback will be isolated from the usage scenario.

<?php
function incrementNum ($number) {
return $number + 1;
}
$numbersPlusOne = array_map(&#39;incrementNum&#39;, [1, 2, 3]);
print_r($numbersPlusOne);

Additional status

Anonymous functions can not only be used as callbacks, but can also be used to attach and encapsulate status for PHP.

In PHP, you must manually call the bindTo() method of the closure object or use the use keyword to attach the state to the PHP closure.

<?php
function enclosePerson ($name) {
return function ($doCommand) use ($name) {
return $name . &#39;, &#39; . $doCommand;
}
}
$clay = enclosePerson(&#39;Clay&#39;);
echo $clay(&#39;get me sweet tea!&#39;);

Get the result:

"Clay, get me sweet tea!"

PHP closures are objects, and each closure instance can use the $this keyword to get the internal state of the closure. The default state of the closure object is useless, only the __invoke() method and the bindTo method.

We can use the bindTo() method to bind the internal state of the Closure object to other objects.

The second parameter of the bindTo() method: Its function is to specify the PHP class to which the object of the binding closure belongs. Therefore, a closure can access protected and private members of the object to which the closure is bound.

PHP frameworks often use the bindTo() method to map routing URLs to anonymous callback functions. By doing this, you can use the $this keyword to reference important application objects in this anonymous function.

Use bindTo() method to attach closure status

<?php
class App
{
protected $routes = [];
protected $responseStatus = &#39;200 OK&#39;;
protected $responseContentType = &#39;text/html&#39;;
protected $responseBody = &#39;Hello world&#39;;
public function addRoute($routePath, $routeCallback){
$this->routes[$routePath] = $routeCallback->bindTo($this, __CLASS__);
}
public function dispatch($currentPath){
foreach($this->routes as $routePath => $callback){
if ($routePath === $currentPath) {
$callback();
}
}
header(&#39;HTTP/1.1&#39; . $this->responseStatus);
header(&#39;Content-type: &#39; . $this->responseContentType);
header(&#39;Content-length&#39; . mb_strlen($this->responseBody));
echo $this->responseBody;
}
}
<br>

<?php
$app = new App();
$app->addRoute(&#39;/user/nesfo&#39;, function () {
$this->responseContentType = &#39;application/json; charset=utf8&#39;;
$this->responseBody = &#39;{"name": "nesfo"}&#39;;
});
$app->dispatch(&#39;/user/nesfo&#39;);

The above is the collection of PHP closure information. We will continue to add relevant information in the future. Thank you for your support of this site!

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