Re: Environment behavior

[Peter Cawley <lua@...>]

If we replace the call to load() and the subsequent execution with
plain Lua code, and desugar the environment references, then your code
is transformed to the following:
-----

local env1 = {print=print, a=1}
local env2 = {print=print, a=2}

do
  local _G = _ENV
  local _ENV -- I'll call this "inner _ENV"
  _G.item = {
    func = function()
      _ENV.print(_ENV.a)
    end,
    subItem = {
      func = function()
        _ENV.print(_ENV.a)
      end,
    }
  }
end

debug.setupvalue(item.func, 1, env1)
debug.setupvalue(item.subItem.func, 1, env2)

item.func()
item.subItem.func()

-----

The inner _ENV is an upvalue of func and subItem.func, and crucially
is a shared upvalue: the first upvalue of func is inner _ENV, and the
first upvalue of subItem.func is inner _ENV. As such,
debug.setupvalue(item.func, 1, x) and
debug.setupvalue(item.subItem.func, 1, x) have the same effect.

On Sat, Dec 7, 2013 at 3:39 PM, Bruno Deligny <bruno.deligny@gmail.com> wrote:
> Hi
>
> I was playing with environements and i dont understand this behavior.
>
> local env1 = {print=print, a=1}
> local env2 = {print=print, a=2}
>
> local component = load([[
>   item = {
>     func = function()
>       print(a)
>     end,
>     subItem = {
>       func = function()
>         print(a)
>       end,
>     }
>   }
>   ]])
>
> component()
>
> debug.setupvalue(item.func, 1, env1)
> debug.setupvalue(item.subItem.func, 1, env2)
>
> item.func()
> item.subItem.func()
>
> This print:
> 2
> 2
>
> I was hoping it printed:
> 1
> 2
>
> It would be great if someone could explain to me how env is propagated.
>
> Thanks
>