Lua元表继承：setmetatable的类层次构建

-- 错误：逐字段把类方法拷进每个实例
function newInstance(name)
    local o = {name = name}
    o.speak = Animal.speak
    o.eat = Animal.eat
    return o
end

local Animal = {}
Animal.__index = Animal
function Animal.new(name)
    return setmetatable({name = name}, Animal)
end
function Animal:speak()
    return self.name .. " makes a sound"
end
local Dog = setmetatable({}, {__index = Animal})
Dog.__index = Dog
function Dog:speak()
    return self.name .. " barks"
end
local d = Dog.new("Rex")
local p = getplayerbyname("oop01")
sendmsg(p, 1, d:speak())