RE: lists with nil play nice for Lua 5.2

["Jerome Vuarand" <jerome.vuarand@...>]

John Belmonte wrote:
> Programming in Lua refers to nil in a list as a "hole", but that is
> from the perspective of Lua's table representation which cannot
> distinguish nil-valued from nonexistent keys.  From the view of the
> list creator, why should either of the following be considered as
> having holes?    

I think part of the problem comes from the fact that some people
distinguish nil-valued from non-existent keys. But the concept of a
non-existent key is not applicable to Lua tables. In Lua a table is an
infinite associative array, with all possible keys having a value. By
default all keys have a nil value. These nils are not explicitly stored,
but that's an implementation detail.

In that context the # operator is not well defined. I see two good
(though not perfect) solutions: either make the table # operator
deterministic (for example return the biggest integer key), or allow
users to override the # operator (that's my prefered solution, since it
would be useful for other problems, like returning the norm of a
vector).