Re: Some conservative Lua metamethod extension proposals

[Dirk Laurie <dirk.laurie@...>]

2018-03-24 8:11 GMT+02:00 Sergey Zakharchenko <doublef.mobile@gmail.com>:

>> IIUC, the OP's "conservative" proposal is merely that 'pairs' should
>> not discard extra arguments, i.e. it should trigger __pairs(tbl,...)
>> rather than just _pairs(tbl).
>
> Note I never wrote about changing meaning of any existing Lua core
> functions.

True, you do not suggest changing what 'pairs' does in the absence of
a metamethod. In fact, I wrote that interpretation  precisely to
emphasize that the proposal that 'pairs' should have a second argument
did not come from you.

> Reread original email if that's not obvious.

Maybe you should take your own advice here. The original says clearly:
"If __pairs is invoked wth a second argument ..."

You can't change the way '__pairs' is called without changing 'pairs'
itself. The manual states: "pairs (t) ... If t has a metamethod
__pairs, calls it with t as argument." I see no way of implementing
your proposal that will not involve a change to "pairs (t[,opt]) ...
If t has a metamethod __pairs, calls it with t and opt as arguments."