Re: magical site for working on common code
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- Subject: Re: magical site for working on common code
- From: Michal Kottman <k0mpjut0r@...>
- Date: 2011年1月05日 15:12:54 +0100
On Tue, 2011年01月04日 at 11:48 +0100, Axel Kittenberger wrote:
> Can someone enlighten me on this bit.
>
> > list_mt.__index = {
> > insert = insert ;
> > append = append ;
> > remove = remove ;
> > length = length ;
> > unpack = unpack ;
> > tostring = table.concat ;
> > sort = table.sort ;
> > }
>
> Why is __index a table and not a function?
The __index can indeed be a table, it is a shortcut for a common
operation - looking up a value in another table. Quoting from PiL [1]:
The use of the __index metamethod for inheritance is so common that Lua
provides a shortcut. Despite the name, the __index metamethod does not
need to be a function: It can be a table, instead. When it is a
function, Lua calls it with the table and the absent key as its
arguments. When it is a table, Lua redoes the access in that table.
The same applies for __newindex. If __newindex is a table, not a
function, all assignments of nonexisting keys are directed into that
table.
[1] http://www.lua.org/pil/13.4.1.html