&gt; and that carries a MAJOR limitation, because the instance of ImplementsFooer (f) inside your function is a copy of the object you called it on. That means you cannot manipulate data-members in interface-functions, even inside your own struct.<p>You can, by doing it like this: <a href="https:&#x2F;&#x2F;play.golang.org&#x2F;p&#x2F;5yXfOf6Y_3" rel="nofollow">https:&#x2F;&#x2F;play.golang.org&#x2F;p&#x2F;5yXfOf6Y_3</a><p>EDIT: I&#x27;ll just file an issue as I doubt the OP is the author.