Re: 'table' as fallback for tables

[Philipp Janda <siffiejoe@...>]

Am 27.06.2016 um 19:29 schröbte Roberto Ierusalimschy:
> > Bingo! I'd say an `n` key with an integer value greater than or
> > equal to 0, but let's not nitpick. I also think this would have been
> > a viable alternative to the sequence concept we now have, because it
> > has some useful properties:
> >
> > *  [...]
>
> Something that seems to be missing in this discussion is constructors:
>
>     l = {1, 2, 3, 4, 5}
>     print(#l)          --> ?  (no 'l.n'...)

We _have_ mentioned this a few times, e.g.:

> *  Counting elements in table literals is cumbersome (Lua could help with that, though).

or in an earlier post:

> Lua already knows how many elements -- including `nil`s -- should be added to a table in a lot of cases, e.g.
>
>     { ... }  -- should be `select('#', ...)`
>     { a = 1, ... }  -- still `select('#', ...)`
>     { 1, f() }  -- should be 1 + number of return values
>     { 1, 2, 3 }  -- should be 3
>     { 1, nil, nil } -- ditto
>     { 1, 2, [4]=4 }  -- 4
>     { 1, 2, [x]=4 }  -- 2, or x if x is an integer > 2
>     { 1, 2, [x]=nil }  -- same

and in one of Tim's posts:

> I’m undecided if a table initializer should set the size: should
> {1,2} have a size of 0 or 2? What about more complex initializers?
> And of course there are issues with non-integral keys etc.

And I'm fine with both options. It all depends on how you want to sell 
the array-style table literal syntax `{ 1, 2, 3 }`:  Is it an array 
constructor (in which case it should set `n`), or is it syntax sugar for 
assigning to small consecutive integer keys (in which case it should 
leave `n` alone).

Array constructors that set `n` would certainly be convenient in some 
situations. E.g., I've recently written a function for unit testing that 
checks that a function yields certain values when resumed with certain 
arguments:

    M.yields( f, { 1, 2 }, M.resp( 2, 3 ),   -- should yield 2, 3
                 { 8, 9 }, M.resp( 9, 10 ),  -- should yield 9, 10
                 { 4, 5 }, M.resp( 5, 6 ) )  -- should return 5, 6

For now I use a hybrid approach for the argument arrays: If there's an 
`n` field, I use it, otherwise I assume a proper sequence.

> -- Roberto

Philipp