Total number of counted occurrences

var c = new Counter[String]
assert c.sum == 0
c.inc_all(["a", "a", "b", "b", "b", "c"])
assert c.sum == 6

Property definitions

counter $ Counter :: sum=
	# Total number of counted occurrences
	#
	# ~~~
	# var c = new Counter[String]
	# assert c.sum == 0
	# c.inc_all(["a", "a", "b", "b", "b", "c"])
	# assert c.sum == 6
	# ~~~
	var sum: Int = 0
lib/counter/counter.nit:41,2--49,17