Re: invalid table index

["Aaron Brown" <arundelo@...>]

Dmitriy Iassenev wrote:

> if we try to assign
>
>   b[nil] = {}
>
> then we get error 'table index is invalid', but if we try
>
>    if b[nil] == nil then
>       ...
>    end
>
> no error is raised. Is it correct behaviour?

Yes.  The manual says:

> An access to an indexed variable t[i] is equivalent to a
> call gettable_event(t,i).

and

> An assignment to an indexed variable t[i] = val is
> equivalent to settable_event(t,i,val).

Both of these functions are

> not defined or callable in Lua.  We use [them] here only
> for explanatory purposes.

Both gettable_event and settable_event use rawget to check
the current value of the table, and rawget's description
says:

> index may be any value

settable_event uses rawset to do the setting, and rawset's
description says:

> index [must be] any value different from nil

See also <http://lua-users.org/lists/lua-l/2006-05/msg00378.html>.

--
Aaron