lua 面向对象实现

虽然lua是一门小巧的胶水语言，但是它也是可以进行面向对象编程的，我们可以实现多继承和单继承，继承都是靠lua的setmetatable实现的。

• 类

  Name = {}
     function Name:new(o) 
      o = o or {}
      setmetatable(o, {__index = self})
      return o
   end
  
   function Name:setName(name)
      self.name = name
   end
  
   function Name:getName()
      return self.Name
  end
  
  -- 在lua中A:b()等价于A.b(self),像标准库中string.len 等价于"xxx":len, 但是为了兼容性更倾向于写作string.len("xxx")
  

• 单继承

  --定义继承
  SpecName = Name:New({age=25})
  function SpecName:setNewName(name)
        if self.getAge() > 9 then
            self:setName(name)
        else
            error("You must give an age!")
        end
  end
  
  function SpecName:getAge()
         return self.age
  end
  

• 多继承

  function search(k, plist)
      for i=1,#plist do
           if plist[i][k] ~= nil then return plist[i][k] end
       end
  end
  
  function createClass(...)
      local args = {...}
      local c = {}
      setmetatable(c, {__index = function(self, k) 
          return search(k, args) 
      end})
  
      c.__index = c
      function c:new(o) 
          o = o or {}
          setmetatable(o, c)
          return o
      end
      return c 
  end
  
  Balance = {balance= 10}
  function Balance:new(o) 
      o = o or {}
      setmetatable(o, {__index = self})
      return o
  end
  
  function Balance:despoit(v)
      self.balance = self.balance + v
  end
  
  function Balance:withDraw(v)
      if self.balance < v then
           error("Bad case")
      else
          self.balance = self.balance - v
      end
  end
  
  Name={}
  function Name:new(o) 
       o = o or {}
       setmetatable(o, {__index = self})
       return o
  end
  
  function Name:setName(name)
      self.name = name
  end
  
  function Name:getName()
      return self.name
  end
  
  c = createClass(Balance, Name)
  c:despoit(100)
  c:withDraw(10)
  print(c.balance)  --> 100
  c:setName("wbz")
  print(c:getName()) --> wbz
  

• 隐藏私有变量

   function newAccount(initBalance)
      local self = {balance=initBalance}
      local withdraw = function(v)
          self.balance = self.balance - v 
      end                    
  
      local deposit = function (v) 
             self.balance = self.balance + v 
      end                    
  
      local getBalance = function()
             return self.balance
      end                    
      return {               
          withdraw=withdraw, 
          deposit = deposit, 
          getBalance = getBalance,    
       }
  end