f := i.M; f(7)  // like i.M(7)
</pre>


<h3 id="Index_expressions">Index expressions</h3>

<p>
A primary expression of the form
</p>

<pre>
a[x]
</pre>

<p>
denotes the element of the array, pointer to array, slice, string or map <code>a</code> indexed by <code>x</code>.
The value <code>x</code> is called the <i>index</i> or <i>map key</i>, respectively.
The following rules apply: