type I interface { m() }

func f(y I) {
	s := y.(string)        // illegal: string does not implement I (missing method m)
	r := y.(io.Reader)     // r has type io.Reader and the dynamic type of y must implement both I and io.Reader
	…
}
</pre>

<p>
A type assertion used in an <a href="#Assignments">assignment</a> or initialization of the special form
</p>

<pre>

type I interface { m() }

func f(y I) {
	s := y.(string)        // illegal: string does not implement I (missing method m)
	r := y.(io.Reader)     // r has type io.Reader and the dynamic type of y must implement both I and io.Reader
	…
}
</pre>

<p>
A type assertion used in an <a href="#Assignment_statements">assignment statement</a> or initialization of the special form
</p>