Sharp = { _val = 1}  --①  父类

function Sharp:new()
    local new_sharp = { }
    self.__index = self  --②，self == Sharp
    setmetatable(new_sharp, self)  --③

    return new_sharp
end

function Sharp:sharp_func()
    print("Sharp call sharp_func")
end

function Sharp:name()
    print("Sharp call name")
end

function Sharp:val()
    print(string.format("Sharp call val %d", self._val))
end


Circle = Sharp:new() --① 子类

function Circle:new()
    local new_circle = {}
    self.__index = self --②，self == Circle
    setmetatable(new_circle, self) --③

    return new_circle
end

--新函数
function Circle:circle_func()
    print("Circle call circle_func")
end

--覆盖函数name
function Circle:name()
    print("Circle call name")
end

--覆盖函数val
function Circle:val()
    print(string.format("Circle call val %d", self._val))
end

local circle = Circle:new()
circle._val = 2 --覆盖赋值
circle:sharp_func() --调用父类函数
circle:circle_func() --调用新函数
circle:name() --调用覆盖函数
circle:val() --调用覆盖函数