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As you say, __index is supposed to be called for non-existent keys. ipairs
though, like a lot of the table library, does not respect __index even if the key is non-existent. An oversight imo, but I guess it must have some advantages (?)...

The main difference is that in letting __ipairs be overriden you can change the order from 1, 2, n to 3, 8, 5, 1 or whatever else tickles your fancy. That will break any existing code which assumes ipairs always starts from 1 and counts up (I've been guilty of making this assumption before), but again I guess it must
have some advantages =P.

- Alex

----- Original Message ----- From: "Ignacio Burgueño" <>
To: "Lua list" <>
Sent: Thursday, February 21, 2008 11:05 PM
Subject: Re: upcoming changes in Lua 5.2 [was Re: Location of a package]

Jérôme Vuarand wrote:
First, I think that the above would be a very welcomed addition to Lua.
Second, in my opinion, __index and __ipairs (whatever the final semantics may be) are not comparable. __index is triggered on access to non-existent keys and __ipairs would be used to redefine the way an array-like table is iterated, right?

Also, using the same metamethod for both cases will make it hard to distinguish when you're indexing a table and when you're going to iterate it.

Ignacio Burgueño