On the BitExpert blog Stephan Hochdörfer shows you how to mock callables in a Zend Expressive application based on a way he found during his own unit testing.

While working with Zend Expressive, a PSR-7 middleware microframework, I wanted to apply some unit testing with a nice coverage to my middlewares. Middlewares are called by the __invoke method if you provide them as an object and not as a closure. [...] Additionally, my middleware implementation does some stuff, but the middleware itself does not return a response, which is fine. Instead, my implementation calls the $next middleware in line.

He finishes the post with a quick example of how to mock out this $next call in his testing using the createPartialMock functionality in PHPUnit. He uses this method to create a mock that covers the __invoke method and returns a ResponseInterface instance of his choosing.

In a new post to his site Joseph Silber looks at a new feature that will be coming with the next release in the PHP 7.x series - PHP 7.1 - the ability to convert a callable type into an actual Closure instance.

With PHP 5.5 going EOL earlier this week and the PHP 7.1 beta expected later this month, now sounds like a good time to look into a neat little feature coming in 7.1: easily converting any callable into a proper Closure using the new Closure::fromCallable() method.

He starts with a quick refresher on what closures/callables are in PHP (or an introduction for those not already familiar) including a simple example with the reject handling on a Laravel collection. He then modifies the example to try to pass in a base PHP function. This doesn't work directly (as it's not technically "callable" how it's expecting) so he wraps the is_float in a closure instead. This is a bit of a hassle and not as reusable so he updates it for PHP 7.1 and uses the Closure::fromCallable handling to make it automatically. He follows this with another example use case: calling a private method with the array of object/method name from inside the class.

Julien Pauli has posted a look at PHP's closures and how they're actually handled internal to the language.

Back in 2009, when PHP 5.3 got released, a new feature (among many others) were introduced : anonymous functions (also called lambdas or closures). The feature was very expected, as closures have proved their utility through several other languages, particularly javascript that web developers master. [...] Let's see together how Closures have been added to PHP, as usual by turning to the truth : the PHP source code.

He starts at the beginning (a good place to start) and talks about the work that needed to be done on the internals before closures could even be introduced. He walks through the changes made to object handling to make them "callable" and the addition of the "zend_closure" object type. He then gets to the part where "the magic happens" and shows how the userland closure is translated and executed. He ends the post with a look at two other topics: scoping with "$this" and the special handling that was needed for reflection and direct calls to "__invoke".

In his latest post Evert Pot wonders if the current implementation of the "Callable" type in PHP is too loose when it comes to what it will accept as a valid callable resource.

PHP got support for closures in version 5.3, and in PHP 5.4 we got support for a callable typehint. [...] All these little changes make it feel more comfortable to apply functional programming concepts to PHP, but occasionally we need to drop back to using less aesthetically pleasing code.

In his examples of "less aesthetically pleasing code" he shows a few different methods that work that aren't the typical closure or object arguments (like passing in an array of object+method name). He also shows an interesting option where you can use a string with a static method call (ex: "MyClass::method") and it will still be accepted. He points out that for this to work correctly in all situations, the call_user_func method should be used, not just calling the input directly.

Freek Lijten has a recent post looking at some of the types of discussions that happen on the php-internals mailing list.

The internals list is the place to be to hear about the current state of PHP. It is one of PHP's many mailing lists, but this is the one where (core) developers discuss new features, current bugs and wild ideas. If you want to keep up with things it is a good idea to sign up, it is not an extremely high volume list and if you ignore the noise it is quite informative. In this article I would like to share examples of stuff typically discussed on the list.

He mentions feature requests in general and, more specifically things like traits support (multiple inheritance), array dereferencing, callable arrays and the debate over the short array syntax.