corresponds to the type argument with which <code>P</code> was
<a href="#Instantiations">instantiated</a>.
</p>

<p>
The capacity of a slice is the number of elements for which there is
space allocated in the underlying array.
At any time the following relationship holds:
</p>

<pre>
0 &lt;= len(s) &lt;= cap(s)
</pre>

<p>
The length of a <code>nil</code> slice, map or channel is 0.