for i, s := range a {
	// type of i is int
	// type of s is string
	// s == a[i]
	g(i, s)
}

var key string
var val interface{}  // element type of m is assignable to val
m := map[string]int{"mon":0, "tue":1, "wed":2, "thu":3, "fri":4, "sat":5, "sun":6}
for key, val = range m {
	h(key, val)
}
// key == last map key encountered in iteration
// val == map[key]

var ch chan Work = producer()

	soon as two field values differ (or all fields have been compared).
	</li>

	<li>
	Array types are comparable if their array element types are comparable.
	Two array values are equal if their corresponding element values are equal.
	The elements are compared in ascending index order, and comparison stops
	as soon as two element values differ (or all elements have been compared).