Cannot unbind $this of closure using $this, this will be an error in PHP 9¶

Description¶

A closure literal that references $this in its body captures the enclosing object when it is created. Rebinding it to null with bindTo() or Closure::bind() would leave the body referencing $this with nothing bound to it, so the operation is refused.

A closure that does not use $this in its body can still be unbound safely; the restriction only applies when $this is actually referenced.

Since PHP 8.5, this operation already emitted an E_WARNING and the bind silently failed, returning null. It is now deprecated and will become a fatal error in PHP 9.0.

Example¶

<?php

class X {
    public $prop = 'hello';

    public function getClosure() {
        return function () {
            return $this->prop;
        };
    }
}

$x = new X;
$fn = $x->getClosure();
$fn2 = $fn->bindTo(null);
var_dump($fn2);

?>

Literal Examples¶

Cannot unbind $this of closure using $this, this will be an error in PHP 9

Solutions¶

If the closure needs to run without an object context, remove every use of $this from its body.
Keep the closure bound to the object and pass the values it needs as parameters instead of relying on unbinding.

See Also¶

Changed Behavior¶

This error may appear following an evolution in behavior, in previous versions. See closure.