Re: best way to add field to userdata?
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- Subject: Re: best way to add field to userdata?
- From: Luis Carvalho <lexcarvalho@...>
- Date: 2010年4月22日 10:02:56 -0400
<snip>
> Alternatively, I could return a table and hang my userdata off that,
> but it seems prone to accidents.
<snip>
You could use the userdatum environment as proxy:
-- image.lua
local env = debug.getfenv
local u = newproxy(true)
local mt = getmetatable(u)
local class = {
resize = function (o, x, y)
local e = env(o)
e.width, e.height = x, y
end,
makepretty = function (o)
print(string.format("image: %d x %d", o.width, o.height))
end
}
mt.__index = function (o, k) return env(o)[k] or class[k] end
mt.__newindex = function (o, k, v) env(o)[k] = v end
function GetImage (w, h)
local o = newproxy(u) -- create or read image
debug.setfenv(o, {width=w, height=h})
return o
end
$ lua -i image.lua
Lua 5.1.4 Copyright (C) 1994-2008 Lua.org, PUC-Rio
> img = GetImage()
> img:resize(100, 200)
> img:makepretty()
image: 100 x 200
> print(img.width, img.height)
100 200
> img.width, img.height = 200, 300
> img:makepretty()
image: 200 x 300
I've implemented in Lua for simplicity, but it's straightforward to adapt it
to C (use lua_getfenv instead of debug.getfenv etc.)
Cheers,
Luis
--
Computers are useless. They can only give you answers.
-- Pablo Picasso
--
Luis Carvalho (Kozure)
lua -e 'print((("lexcarvalho@NO.gmail.SPAM.com"):gsub("(%u+%.)","")))'