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- Subject: Re: Iterating pairs of keys from a table
- From: Tim Hill <drtimhill@...>
- Date: Thu, 2 Mar 2017 02:09:11 -0800
> On Feb 28, 2017, at 9:43 PM, Dirk Laurie <email@example.com> wrote:
> If you must have an iterator factory, and wish to avoid a coroutine
> (damn! I so seldom have good reason to use one, your problem
> seemed to be a case in point), it is possible to do it all in a single
> generic `for` by making your routine stateless. Exercise for the
> keypairs = function(tbl)
> return function(tbl,k1,k2)
> -- no upvalues required
> return k1,k2
Well, you have me beaten. For a start, I was under the impression Lua only passed two arguments to the iterator function, yet you have three? Clearly I’m missing something.
I did look at cunning ways to bury the state is the (s, v) pair maintained by the for loop as a way to avoid upvalues, but I didn’t really see any advantage over upvalues from a performance perspective.