RE: Metatables

[Eric Tetz <erictetz@...>]

Well, I've found a situation for which my 'proxy' object cannot help: operator ==. In the
previously mentioned language (FOOBAR) we can have:

  if state == 0 then
   state = state + 1
  end

Where 'state' need not exist before the boolean expression.  If it doesn't exist, it is created
and initialized to zero, so this boolean would evaluate to true.

Without a 'metaevent' for ==, I don't know what to do.  The proxy gets me 99% of the way there,
but without this last 1% I'll be forced to use plan B.  Plan B is to analyze the FOOBAR source,
trying to guess which variables in which expressions are not initialized.  This will be impossible
to do with 100% accuracy, because FOOBAR variables are all global, and the order in which a
project's scripts are run is non-deterministic (event driven). Is 'state = 10' the first-time
initialization of 'state'? It depends on whether the script containing this line executes before a
script that uses 'state' in an expression.

Anyway, any ideas are welcome.  I've reposted the proxy code I'm using below.

Cheers,
Eric

-- proxy.lua

local
  proxy_toval,
  proxy_tonum, 
  proxy_tostr, 
  proxy_metatable

function proxy_toval(p,val)
  if type(p) == "table" and metatable(p) == proxy_metatable then
    setglobal (p.name, val)
    return val 
  else
    return p
  end
end

function proxy_tonum(p)
  return proxy_toval(p,0)
end

function proxy_tostr(p)
  return proxy_toval(p,"")
end

proxy_metatable = {
  add = function(l,r) return proxy_tonum(l) + proxy_tonum(r) end,
  sub = function(l,r) return proxy_tonum(l) - proxy_tonum(r) end,
  mul = function(l,r) return proxy_tonum(l) * proxy_tonum(r) end,
  div = function(l,r) return proxy_tonum(l) / proxy_tonum(r) end,
  pow = function(l,r) return proxy_tonum(l) ^ proxy_tonum(r) end,
  unm = function(o) setglobal(o.name, 0) return 0  end, 
  concat = function(l,r) return proxy_tostr(l)..proxy_tostr(r) end,
  settable = function(t,k,v) 
    local nt = {}
    rawset (nt, k, v)
    setglobal (t.name, nt)
  end,
}

metatable (
  globals(), {
  index = function(t,k) 
    local proxy = { name = k }
    metatable (proxy, proxy_metatable)
    rawset (t, k, proxy) 
    return proxy 
  end,
  })


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