Re: Definition of a sequence

[Dirk Laurie <dirk.laurie@...>]

2015-06-11 10:29 GMT+02:00 Mike <lua-l@inbox.ru>:

> I cannot guess the exact rule for the length operator

The rule is implementation-dependent, but the Lua implementation
has not recently changed.

In the Lua 5.1 manual, the following boundary property was
guaranteed:

    t[#t] is not nil, but t[#t+1] is.

This is no longer documented, perhaps because the user can now
supply a __len that does not have that property.

The implementation does a binary search, once indices i and j
have been found with the property that i<j, t[i] is not nil, t[j] is nil.

The last index in the "array part" of the table is always the starting
value for either i or j, with respectively doubling or halving used to find
the other.

The difference you observe is caused by different sizes of the
array part.

An implementation change that has been proposed on this list
is the following: store the previous value of #t and check whether
it still has the boundary property. This gives O(1) time in the
common case when the table size has not changed, but