Re: Weird __newindex behaviour

[Oliver Kroth <oliver.kroth@...>]

Oh,

now I see better. You were talking about
tab.test = nil, not return tab.test (which is nil)
But the anwser is simple too:
You set tab.test = 123, calling your metatable's __newindex.
Then you set it to nil, as it existing, __newindex isn_t called.
Becasue it got nil, it disappeared from the table.
The next table.test = nil calls __newindex() as tab.test is now new.

--
Oliver


Am 22.09.2015 um 17:41 schrieb Scott Morgan:
> Seeing the following behaviour on various version of Lua:
>
> Lua 5.2.2  Copyright (C) 1994-2013 Lua.org, PUC-Rio
> ~ mt = { __newindex = function(t,k,v)
> ~~ print("Setting :", k, "to", v)
> ~~ rawset(t,k,v)
> ~~ end }
> ~ tab = setmetatable({},mt)
> ~ return tab
> table: 0x671df0
> ~ return tab.test
> nil
> ~ tab.test = 123
> Setting :	test	to	123
> ~ tab.test = nil
> ~ tab.test = nil
> Setting :	test	to	nil
> ~ tab.test = nil
> Setting :	test	to	nil
> ~ tab.test = 321
> Setting :	test	to	321
> ~ return tab.test
> 321
> ~ tab.test = nil
> ~ return tab.test
> nil
> ~ tab.test = nil
> Setting :	test	to	nil
>
> Why isn't the first `tab.test = nil` event being handled by the
> metatable? As mentioned, I'm seeing this across Lua versions, 5.1, 5.2
> (as above) and 5.3 (and different OS's/compilers)
>
> It's weird because, surely, if this is a bug, it has already been seen.
> It's such a common pattern. I must be doing something wrong here?
>
> Scott