[Rd] Define 'in' for new class

[peter dalgaard]

On 12 Aug 2014, at 08:29 , Simon Knapp <sleepingwell at gmail.com> wrote:

> Hi List,
> 
> Is it possible to define how 'in' works for an object of a specific class
> (to achieve a similar result to implementing the iterator protocol in a
> class Python)?
> 

No, because 'in' doesn't really exist, it is "syntactic sugar" to sweeten a call to the "for" function with its three arguments. E.g.

> `for`(i,1:2,print(i))
[1] 1
[1] 2

So what you're really asking for is something like a `for` with class dispatch or the two first arguments replaced by an iterator mechanism. That's not in the cards, at least at the moment, but I suppose it isn't completely out of the question either -- ideas of this sort get bandied around occasionally. It would require changes to R's internals; it is not something you can do in (say) a package.


> Cheers,
> Simon Knapp
> 
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> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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