Re: 'table' as fallback for tables
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- Subject: Re: 'table' as fallback for tables
- From: Philipp Janda <siffiejoe@...>
- Date: 2016年6月28日 01:59:53 +0200
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