The : operator

The : operator is used to call methods on an object. Using the : operator requires that the __index metamethod is defined as the metatable itself. If the __index metamethod is set to the metatable itself, the result is to translate t:test(123) into mt["test"](t,123), where mt is the metatable which has been defined using set metatable for the table t.

mt={}
mt.__index = mt
mt.test = function(self,value)
if self.total == null then
self.total = 0
end
self.total = self.total + value
return self.total

end	
t={}	
setmetatable(t,mt)	--> x = 123
x = t:test(123)	
y = t:test(1)	--> y = 124
z = t.total	--> z = 124