They cannot be the types of values or variables, or components of other,
non-interface types.
</p>

<pre>
var x Float                     // illegal: Float is not a basic interface

var x interface{} = Float(nil)  // illegal

type Floatish struct {
	f Float                 // illegal
}
</pre>

<p>
An interface type <code>T</code> may not embed a type element