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2011/10/29 Axel Kittenberger <axkibe@gmail.com>:

> # is not biuniquely defined for non linear tables that do not go from
> 1...n.  You can read up the exact definition of #, but usually just
> don't do it for something that is not defined 1..n.
>
…
> The length of a table t is defined to be any integer index n such that
> t[n] is not nil and t[n+1] is nil; moreover, if t[1] is nil, n can be
> zero.

Lua 5.2 beta pitches it more strongly: # is _undefined_ for tables
that do not go from 1...n, unless you have defined a __len metamethod.
 So that last sentence is no longer valid.

Dirk