Using `$this` in an anonymous function in PHP pre 5.4.0
The PHP manual states
It is not possible to use
$thisfrom anonymous function before PHP 5.4.0
on the anonymous functions page. But I have found I can make it work by assigning $this to a variable and passing the variable to a use statement at the function definition.
$CI = $this;
$callback = function () use ($CI) {
$CI->public_method();
};
Is this a good practice?
Is there a better way to access $this inside an anonymous function using PHP 5.3?
Answer
It will fail when you try to call a protected or private method on it, because using it that way counts as calling from the outside. There is no way to work around this in 5.3 as far as I know, but come PHP 5.4, it will work as expected, out of the box:
class Hello {
private $message = "Hello world\n";
public function createClosure() {
return function() {
echo $this->message;
};
}
}
$hello = new Hello();
$helloPrinter = $hello->createClosure();
$helloPrinter(); // outputs "Hello world"
Even more, you will be able to change what $this points to at runtime, for anonymus functions (closure rebinding):
class Hello {
private $message = "Hello world\n";
public function createClosure() {
return function() {
echo $this->message;
};
}
}
class Bye {
private $message = "Bye world\n";
}
$hello = new Hello();
$helloPrinter = $hello->createClosure();
$bye = new Bye();
$byePrinter = $helloPrinter->bindTo($bye, $bye);
$byePrinter(); // outputs "Bye world"
Effectively, anonymus functions will have a bindTo() method, where the first parameter can be used to specify what $this points to, and the second parameter controls what should the visibility level be. If you omit the second parameter, the visibility will be like calling from the "outside", eg. only public properties can be accessed. Also make note of the way bindTo works, it does not modify the original function, it returns a new one.