Message-ID: <4A341133.4090402@stats.uwo.ca>
Date: 2009-06-13T20:50:59Z
From: Duncan Murdoch
Subject: conditional dependencies & loading
In-Reply-To: <c2350ba40906131339g69cd80d9k8619c5dc83734242@mail.gmail.com>
Kynn Jones wrote:
> Hi!
>
> I'm working on a package that must convert data to and from JSON. For this,
> it can use either the rjson package, or preferably, the faster RJSONIO
> package.
>
> I have two related questions about this.
>
> First, how can I specify that the package depends on *either* RJSONIO *or*
> rjson? (I.e. both are not required.)
>
I don't think you can do that. You can say it suggests both, but it
will not automatically fail to install if they are not found. You need
to put a check into your .onLoad function to fail with an error if
neither is found.
> Second, what's the best-practice R idiom for such conditional loading? I.e.
> I'm looking for R's equivalent of Python's
>
>
>>>> try:
>>>>
> ... import json
> ... except ImportError:
> ... import simplejson as json
>
>
You would use something like
if (!require(RJSONIO) && !require(rjson)) stop("Need one of RJSONIO or
rjson")
in your .onLoad function.
Duncan Murdoch
> Thanks!
>
> kynn
>
> [[alternative HTML version deleted]]
>
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