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- Subject: Re: '__iter', yet again!
- From: Geoff Leyland <geoff_leyland@...>
- Date: Thu, 17 Dec 2009 10:57:34 +1300
On 17/12/2009, at 10:29 AM, John Hind wrote:
> No! You cannot implement '__iter' by re-writing pairs and ipairs, that is
> the competing (and I agree , trivial) '__pairs' & '__ipairs' proposal which
> provide metatable customisation of pairs and ipairs similar to the way
> '__tostring' customises the "tostring" function.
> '__iter' is intended to enable you to write:
> for v in obj do ... end
> Where 'obj' is a table with a metatable containing a function similar to
> 'pairs' keyed with '__iter'. You have to modify the parser and probably the
> byte code interpreter to implement this.
Ok, I misunderstood. To see if I'm now on the right track, am I right in thinking that:
for v in obj do ... end
iterates through obj's "default" list, in a default order and only ever provides one value to the iteration?
I can see where you're coming from in terms of simple syntax, but that's a fairly constrained interface and I tend to find that I need things like:
for v, u, w in obj:give_me_several_values() do ... end
for v in obj:choose_an_order() do ... end
for v in obj:choose_a_set_of_elements() do ... end
If you're worried about polluting the object's namespace, is a syntax like
for v in elements(obj) do ... end
really too ugly?