Does PHP have lexical scope in anonymous functions / closures?

Question

I'm using PHP 5.4 and wondering if the anonymous functions I'm making have lexical scoping?

I.e. If I have a controller method:

protected function _pre() {
    $this->require = new Access_Factory(function($url) {
        $this->redirect($url);
    });
}

When the Access Factory calls the function it was passed, will the $this refer to the Controller where it was defined?

Answer 1

Anonymous functions don't use lexical scoping, but $this is a special case and will automatically be available inside the function as of 5.4.0. Your code should work as expected, but it will not be portable to older PHP versions.

---

The following will not work:

protected function _pre() {
    $methodScopeVariable = 'whatever';
    $this->require = new Access_Factory(function($url) {
        echo $methodScopeVariable;
    });
}

Instead, if you want to inject variables into the closure's scope, you can use the use keyword. The following will work:

protected function _pre() {
    $methodScopeVariable = 'whatever';
    $this->require = new Access_Factory(function($url) use ($methodScopeVariable) {
        echo $methodScopeVariable;
    });
}

---

In 5.3.x, you can get access to $this with the following workaround:

protected function _pre() {
    $controller = $this;
    $this->require = new Access_Factory(function($url) use ($controller) {
        $controller->redirect($url);
    });
}

See this question and its answers for more details.

Answer 2

In short, no, but you can access public methods & functions by passing it:

$that = $this;
$this->require = new Access_Factory(function($url) use ($that) {
    $that->redirect($url);
});

edit: as Matt rightly pointed out support for $this in closures started with PHP 5.4