<p>
The built-in functions <code>len</code> and <code>cap</code> take arguments
of various types and return a result of type <code>int</code>.
The implementation guarantees that the result always fits into an <code>int</code>.
</p>

<pre class="grammar">
Call      Argument type    Result

len(s)    string type      string length in bytes
          [n]T, *[n]T      array length (== n)

</pre>

<p>
If the capacity of <code>s</code> is not large enough to fit the additional
values, <code>append</code> <a href="#Allocation">allocates</a> a new, sufficiently large underlying
array that fits both the existing slice elements and the additional values.
Otherwise, <code>append</code> re-uses the underlying array.
</p>

<pre>
s0 := []int{0, 0}