OOP

Intro

Lua的对象的本质其实依然是一张表

Class

Lua没有类的概念，但是可以参考基于原型的语言（prototype-based language）来模拟类 setmetatable(A, {__index = B}) 即可完成类B的对象A的创建


Account = { balance = 0,
		    withdraw = function(self, v)
			    if (v > self.balance) then error "insufficient funds" end
					self.balance = self.balance - v
				end,

            __tostring = function (acc)
                return ("Balance: " .. acc.balance)
            end,

            -- __index = Account,
}

function Account:deposit (v)
	self.balance = self.balance + v
end


function Account:new (o)
    o = o or {} -- 若创建时o为nil则自动创建一个空表
    self.__index = self
    setmetatable(o, self)
    return o
end

local a = Account:new()
a:deposit(100)
print(a)

Inheritance

直接在新建的对象中创建新字段 / 覆盖原有方法的字段

⚠️

注意：元方法字段无法被继承，需要自己在子类中显式重写

补充：另一种实现方式是直接设置新的类的metatable为要继承的类，__index设置为自己即可


SpecialAccount = Account:new({
	limit = 1000.00,
	__tostring = Account.__tostring
})

-- override 'new', but not necessary
function SpecialAccount:new(o)
    o = Account:new(o)
    self.__index = self
    setmetatable(o, self)
    return o
end

s = SpecialAccount:new()
function SpecialAccount:withdraw (v)
    if (v - self.balance > self:getlimit()) then
        error "insufficient funds : out of limit"
    end
    self.balance = self.balance - v
end

function SpecialAccount:getlimit ()
    return self.limit or 0
end

s:withdraw(100)
s:deposit(500)
print(s)  -- Balance: 400


local DerivedSpecialAccount = SpecialAccount:new({limit = 2000, __tostring = SpecialAccount.__tostring})
local dsa = DerivedSpecialAccount:new()
dsa:withdraw(1050)
dsa:deposit(100)
print(dsa)

Multiple Inheritance

将其他类的方法组合到子类，勉强实现一下多重继承