<p class="rule">
The completion of a single call of <code>f()</code> from <code>once.Do(f)</code>
is synchronized before the return of any call of <code>once.Do(f)</code>.
</p>

<p>
In this program:
</p>

<pre>
var a string
var once sync.Once

func setup() {
	a = "hello, world"
}

func doprint() {
	once.Do(setup)
	print(a)
}

func twoprint() {
	go doprint()

one iteration variable is permitted, otherwise there may be up to two.
If the last iteration variable is the <a href="#Blank_identifier">blank identifier</a>,
the range clause is equivalent to the same clause without that identifier.
</p>

<p>
The range expression <code>x</code> is evaluated once before beginning the loop,
with one exception: if at most one iteration variable is present and

stands for one item (parameter or result) of the specified type and
all non-<a href="#Blank_identifier">blank</a> names in the signature
must be <a href="#Uniqueness_of_identifiers">unique</a>.
If absent, each type stands for one item of that type.
Parameter and result
lists are always parenthesized except that if there is exactly
one unnamed result it may be written as an unparenthesized type.