Re: Strong tables in Lua 5.4

[Philipp Janda <siffiejoe@...>]

Am 16.03.2018 um 12:31 schröbte Dirk Laurie:
> Define a "strong table" as one in which 't[k]=nil' does not remove the
> key, it stores nil.
>
> In Lua 5.4 (work1), all or no tables are strong, depending on
> LUA_NILINTABLE. A new keyword 'undef' is needed to remove a key from a
> strong table.
>
> If instead of that, a hitherto unused letter of the __mode metafield
> (say 'n') is used to indicate whether a table is strong, then
> (a) strong and non-strong tables could coexist in the same code;
> (b) no compiler variable would be needed
>
> To remove a key from a strong table, a function table.undef could be
> supplied that temporarily replaces 'n' in __mode by a neutral letter
> and does a rawset.

This would make code that is always wrong (leaks table keys) in 5.4work1 
only sometimes wrong with "strong" tables. I'm not sure that is better, 
because you'd have to fix it either way, and you would have less 
pressure to do so.

I think that storing nils in tables is worth a break in backwards 
compatibility. We should just call it Lua 6.0 and design a nicer syntax 
for deleting keys.


Philipp