跟我一起了解Lua语言中的_index,newindex,rawget和rawset

标签：lua   c++   

前言：理解Lua语言中的__index, __newindex, rawget和 rawset

Window = {}
Window.prototype = 
{
x = 0 ,
y = 0 ,
width = 100 ,
height = 100,
}
Window.mt = {}
function Window.new(o)
setmetatable(o ,Window.mt)
return o
end
Window.mt.__index = Window.prototype


Window.mt.__newindex = function (table ,key ,value)
if key == "wangbin" then
rawset(table ,"wangbin" ,"yes,i am")
end
end
下面是测试：
local w = Window.new{x = 10 ,y = 20}
w.wangbin = "55"
print(w.wangbin)

Window = {}


Window.prototype =
{
x = 0 ,
y = 0 ,
width = 100 ,
height = 100,
}
Window.mt = {}
function Window.new(o)
setmetatable(o ,Window.mt)
return o
end
Window.mt.__index = function (t ,key)
-- body
return 1000
end
local w = Window.new{x = 10 ,y = 20}
print(w.wangbin)

Window.mt = {}
function Window.new(o)
setmetatable(o ,Window.mt)
return o
end
Window.mt.__index = function (t ,key)
return 1000
end
Window.mt.__newindex = function (table ,key ,value)
if key == "wangbin" then
rawset(table ,"wangbin" ,"yes,i am")
end
end
下面是测试
local w = Window.new{x = 10 ,y = 20}
w.wangbin = "55"
print(w.wangbin)

ok，这里的打印结果是:yes,i am。w这个表里本来没有wangbin这个元素的，我们重写了元表中__newindex，并在__newindex方法中重新进行赋值操作，然后，我们对这个本不存在的原色w.wangbin进行赋值时，执行__newindex方法的赋值操作，最后，打印结果便是:yes,i am

Window = {}


Window.prototype = 
{
x = 0 ,
y = 0 ,
width = 100 ,
height = 100,
}
Window.mt = {}
function Window.new(o)
setmetatable(o ,Window.mt)
return o
end
Window.mt.__index = function (t ,key)
return 1000
end
Window.mt.__newindex = function (table ,key ,value)
if key == "wangbin" then
rawset(table ,"wangbin" ,"yes,i am")
end
end
w = Window.new{x = 10 ,y = 20}
print(rawget(w ,w.wangbin))

Window = {}
Window.prototype = 
{
x = 0 ,
y = 0 ,
width = 100 ,
height = 100,
}
Window.mt = {}
function Window.new(o)
setmetatable(o ,Window.mt)
return o
end
Window.mt.__index = function (t ,key)
return 1000
end
Window.mt.__newindex = function (table ,key ,value)
table.key = "yes,i am"
end
w = Window.new{x = 10 ,y = 20}
w.wangbin = "55"

跟我一起了解Lua语言中的_index,newindex,rawget和rawset

标签：lua   c++   

原文地址：http://blog.csdn.net/zwc2xm/article/details/47252969