Re: ipairs in Lua 5.3.0-alpha

[Roberto Ierusalimschy <roberto@...>]

> I would thus conclude that my previously brought up argument in 3. a)
> is valid, but only results in a slowdown of a factor of 1.33
> (51.611 seconds versus 38.697 seconds).

If the goal is only to reduce calls to length, another option would be
to modify ipairs so that it stops in the first nil entry with an index
larger than #t. That would have some nice properties:

- The length operator would be called only for nil elements (plus one
extra call at the end).

- It is more compatible with the original semantics of ipairs for
regular tables. (If no metamethods, it stops in the first nil, which
should be larger than #t in a proper sequence anyway.)

- It allows "unlimited" traversal, where you don't know the length
beforehand (make #t == 0 so that it will stop at the first nil element).

-- Roberto