RE: How to hook a lua variable accessing

["Huang, Baiyan" <Baiyan.Huang@...>]

Cool!  Steve, 
How could I neglect  the power of meta table:) Thanks!

-Baiyan   
      

-----Original Message-----
From: lua-l-bounces@lists.lua.org [mailto:lua-l-bounces@lists.lua.org] On Behalf Of steve donovan
Sent: 23 January 2013 16:23
To: Lua mailing list
Subject: Re: How to hook a lua variable accessing

On Wed, Jan 23, 2013 at 10:10 AM, Huang, Baiyan
<Baiyan.Huang@morganstanley.com> wrote:
> Then I want to remove this global variable, but I want to give a buffer time
> for our user to off board, so I stage the change and firstly it will emit an
> warning if user is using this global variable.  Is there a way to achieve
> this without using LuaMacros?

Sure, but you have to attach a metatable to _G, that tracks
__newindex.  For this to fire on GLOBAL_VARIABLE this variable must
not be in _G already, so __index is defined to look it up.

Something like this:

local global_variable = 'boo'

local function message(writing)
   print 'you are still using GLOBAL_VARIABLE'
end

setmetatable(_G,{
   __index = function (t, k)
       if k == 'GLOBAL_VARIABLE' then
            message(false)
            return global_variable
        end
  end;
  __newindex = function(t,k,v)
     if k == 'GLOBAL_VARIABLE' then
         message(true)
         global_variable = v
     end
 end;
})

Easy to generalize for a whole bunch of 'globals' that you want to deprecate.

steve d.



--------------------------------------------------------------------------------

NOTICE: Morgan Stanley is not acting as a municipal advisor and the opinions or views contained herein are not intended to be, and do not constitute, advice within the meaning of Section 975 of the Dodd-Frank Wall Street Reform and Consumer Protection Act. If you have received this communication in error, please destroy all electronic and paper copies and notify the sender immediately. Mistransmission is not intended to waive confidentiality or privilege. Morgan Stanley reserves the right, to the extent permitted under applicable law, to monitor electronic communications. This message is subject to terms available at the following link: http://www.morganstanley.com/disclaimers. If you cannot access these links, please notify us by reply message and we will send the contents to you. By messaging with Morgan Stanley you consent to the foregoing.