a <a href="#Run_time_panics">run-time panic</a> occurs.
In other words, even though the dynamic type of <code>x</code>
is known only at run time, the type of <code>x.(T)</code> is
known to be <code>T</code> in a correct program.
</p>

<pre>
var x interface{} = 7          // x has dynamic type int and value 7
i := x.(int)                   // i has type int and value 7

type I interface { m() }

func f(y I) {

<h3 id="Language_versions">Language versions</h3>

<p>
The <a href="/doc/go1compat">Go 1 compatibility guarantee</a> ensures that
programs written to the Go 1 specification will continue to compile and run
correctly, unchanged, over the lifetime of that specification.
More generally, as adjustments are made and features added to the language,
the compatibility guarantee ensures that a Go program that works with a