not reloading local variables from shared memory.
For example, a compiler must not discard <code>i</code> and reload it
a second time from <code>*p</code> in this program:
</p>

<pre>
i := *p
if i &lt; 0 || i &gt;= len(funcs) {
	panic("invalid function index")
}
... complex code ...
// compiler must NOT reload i = *p here
funcs[i]()
</pre>

<p>

and whose length and capacity are <code>len</code>.
<code>Slice(ptr, len)</code> is equivalent to
</p>

<pre>
(*[len]ArbitraryType)(unsafe.Pointer(ptr))[:]
</pre>

<p>
except that, as a special case, if <code>ptr</code>
is <code>nil</code> and <code>len</code> is zero,
<code>Slice</code> returns <code>nil</code>.
</p>

<p>

a2 := [2]byte(s)         // a2[0] == s[0]
a4 := [4]byte(s)         // panics: len([4]byte) > len(s)

s0 := (*[0]byte)(s)      // s0 != nil
s1 := (*[1]byte)(s[1:])  // &s1[0] == &s[1]
s2 := (*[2]byte)(s)      // &s2[0] == &s[0]
s4 := (*[4]byte)(s)      // panics: len([4]byte) > len(s)

var t []string
t0 := [0]string(t)       // ok for nil slice t