php-ext-thisrc

PHP extension to get refcount of $this.

This extension only adds one new function thisrc() : int. It returns the refcount of $this when called from a class.

Why require $this instead of arbitrary argument?

When the parameter is passed to another function, the refcount increases. This might cause confusing behaviour. Calling the function without passing any references is more reliable.

When is refcount information useful?

Consider an immutable value class with methods that return a modified version:

class Foo {
	private $inner;

	public function __construct(int $inner) {
		$this->inner = $inner;
	}

	public function plus(int $value) : Foo {
		return new Foo($this->inner + $value);
	}

	public function times(int $value) : Foo {
		return new Foo($this->inner - $value);
	}
}

$three = new Foo(3);
$sixteen = $three->plus(5)->times(2);

This creases an intermediate object Foo(8) in the call chain. If used in hot code, this allocation could be optimized away:

public function plus(int $value) : Foo {
	if(thisrc() === 1) {
		$this->inner += $value;
		return $this;
	} else {
		return new Foo($this->inner + $value);
	}
}

Then only one new Foo object is created in the call chain that creates $sixteen, avoiding the allocation for the intermediate Foo(8).