Re: callstack recursive environment

[Steve Litt <slitt@...>]

A-greed!!!

What you said. I didn't know about strict.lua, and it's a valuable
addition to my knowledge that I'll use every time, same way I always
use "use strict" in Perl.

Graham, thanks for pointing this out!

SteveT

On Thu, 29 Mar 2012 09:18:21 -0700 (PDT)
codemonkey Monkey <thecodemonkey@rocketmail.com> wrote:

> 
> 
> Oh, excellent.  Thanks for posting this :)
> 
> I'm of the opinion that all variables should be declared, period.
> Not doing so leaves one open to typo errors that aren't discovered
> until obscure conditions happen at runtime, unless one has 100% test
> coverage of their code, which is generally not possible to accomplish.
> 
> 
> CM
> 
> 
> 
> ________________________________
>  From: Graham Wakefield <wakefield@mat.ucsb.edu>
> To: Lua mailing list <lua-l@lists.lua.org> 
> Sent: Wednesday, March 28, 2012 3:38 PM
> Subject: Re: callstack recursive environment
>  
> 
> 
> On Mar 28, 2012, at 11:46 AM, Steve Litt wrote:
> 
> > It sounds to me, from your words above, that all globals go in _G.
> > Now watch this...
> > 
> > Give _G a metatable that, when you're in diagnostic mode, errors
> > out on every global not specifically declared in _G's metatable ...
> 
> > SteveT
> > 
> 
> I think what you are describing is what strict.lua does, more or less:
> 
> 
> 
> --
> -- strict.lua
> -- checks uses of undeclared global variables
> -- All global variables must be 'declared' through a regular
> assignment -- (even assigning nil will do) in a main chunk before
> being used -- anywhere or assigned to inside a function.
> --
> 
> local getinfo, error, rawset, rawget = debug.getinfo, error, rawset,
> rawget
> 
> local mt = getmetatable(_G)
> if mt == nil then
>   mt = {}
>   setmetatable(_G, mt)
> end
> 
> mt.__declared = {}
> 
> local function what ()
>   local d = getinfo(3, "S")
>   return d and d.what or "C"
> end
> 
> mt.__newindex = function (t, n, v)
>   if not mt.__declared[n] then
>     local w = what()
>     if w ~= "main" and w ~= "C" then
>       error("assign to undeclared variable '"..n.."'", 2)
>     end
>     mt.__declared[n] = true
>   end
>   rawset(t, n, v)
> end
>   
> mt.__index = function (t, n)
>   if not mt.__declared[n] and what() ~= "C" then
>     error("variable '"..n.."' is not declared", 2)
>   end
>   return rawget(t, n)
> end