Re: Some conservative Lua metamethod extension proposals

[Philipp Janda <siffiejoe@...>]

Am 23.03.2018 um 09:41 schröbte Sergey Zakharchenko:
> Dirk,
>
> > > If __pairs is invoked wth a second argument equal to the special value
> > > false, the caller is not interested in values (only in keys), so the
> > > returned iterator may returned any value, including nil, or no value
> > > at all, for them.
> >
> > You can already write "for k in pairs(tbl,false) do ... end".
>
> Sure I can. However, certain kinds of (heavily meta) tables may have a
> high cost of value retrieval, which this proposal aims to eliminate.

When using the `pairs` function, I expect getting pairs. An iterator 
factory for keys only would better be called `keys()`. 
Implementation-wise it could look for a `__keys` metamethod for those 
performance critical cases and fall back to the `pairs` protocol but 
dropping the second value.

Philipp