Re: Lua 5.2 - emulation of old setfenv

[Lorenzo Donati <lorenzodonatibz@...>]

Peter Cawley wrote:
> _ENV is always the first upvalue of a chunk (i.e. a function created
> by passing a piece of non-bytecode source code to lua_load), but this
> is not true for functions in general. Functions in general may or may
> not have an upvalue called _ENV, which may or may not be a shared
> upvalue, and if they do have an _ENV upvalue, it doesn't have to be
> the 1st upvalue.

Thanks! This clarifies why my attempt didn't work!

The specific use case I'm trying to tackle is the following (simplified):

----------------------------------------------
local function Runner(func)

local env = {}
-- env is populated here with entries, e.g.:
env.Log = function(msg)
  -- store away the message
end
-- ...
local oldenv = getfenv(func)
-- set a metatable so that oldenv is still
-- visible, but entries in env "override" those
-- in oldenv
setmetatable( env, { __index = oldenv } )
setfenv(func, env)

func()

-- here env is used with
-- any possible modification done
-- by running func
-- ...
end

Then Runner is called like this:


Runner( function()
  -- anonymous function which performs some task
  -- using the facilities provided by "Runner", e.g.:
  Log 'initializing the transmogryfier...'
 -- ...

end)
----------------------------------------------------

So I hope there is a way to replace setfenv/getfenv easily in 5.2 (at 
least for this use case), otherwise I have to rewrite those scripts in a 
different way.

--
Lorenzo