Lua 更多元方法
示例
元方法还有很多,其中一些是算术的(例如加法,减法,乘法),还有按位运算(和,或,或,移位),比较(<,>)以及基本类型运算,例如==和#(相等和长)。让我们构建一个支持许多这些操作的类:对有理算术的调用。尽管这是非常基本的,但它说明了这个想法。
local meta = { -- string representation __tostring = function(self) return string.format("%s/%s", self.num, self.den) end, -- addition of two rationals __add = function(self, rhs) local num =self.num*rhs.den+rhs.num* self.den local den =self.den* rhs.den return new_rational(num, den) end, -- equality __eq = function(self, rhs) returnself.num==rhs.numandself.den== rhs.den end } -- a function for the creation of new rationals function new_rational(num, den) local self = { num = num, den = den } setmetatable(self, meta) return self end local r1 = new_rational(1, 2) print(r1) -- 1/2 local r2 = new_rational(1, 3) print(r1 + r2) -- 5/6 local r3 = new_rational(1, 2) print(r1 == r3) -- true -- this would be the behaviour if we hadn't implemented the __eq metamethod. -- this compares the actual tables, which are different print(rawequal(r1, r3)) -- false