#[PHP, size 23, by bwoebi](https://codegolf.stackexchange.com/a/41063/25180)

    echo@$c=b,$b.$$c=$c.$c;

I'm confused by why `echo@$$c=b,$$c.$$cc.=b;` doesn't work, while calling `echo@$$c=b,${""}.$$cc.=b;` directly does.