On Feb 22, 2013, at 6:13 PM, Hadley Wickham wrote:
> Hi Davor,
>
> To the best of my knowledge, there's only one way to use functions
> from a suggested package: with require:
>
> if (require("suggested_package")) {
> function_from_suggested_package()
> } else {
> stop("suggested package not installed")
> }
>
> Unfortunately I don't think there's any way to use a suggested package
> without polluting the search path.
I've always wondered: How does lattice manage to use grid functions without
putting them on the search path?
--
David
>
> Hadley
>
> On Fri, Feb 22, 2013 at 6:26 PM, Davor Cubranic <cubra...@stat.ubc.ca> wrote:
>> If in my package "Foo" I call a function from another package "Bar" if it's
>> available, according to R-exts, this sounds like I should include "Suggests:
>> Bar" in package Foo's description. But the manual is silent on how to treat
>> Bar's namespace. Should I import it? If so, should this be conditional or
>> unconditional? There is a thread from 2008 in which Duncan Murdoch suggests
>> trying conditionally importing a package if it's installed, with the caveat
>> "If this is allowed"
>> (http://tolstoy.newcastle.edu.au/R/e5/devel/08/10/0488.html). This appears
>> to work in current release of R, 2.15.2, but I'm still not clear if it's
>> officially allowed, much less recommended.
>>
>> The manual also says:
>>
>>> If a package only needs a few objects from another package it can use a
>>> fully qualified variable reference in the code instead of a formal import.
>>> A fully qualified reference to the function f in package foo is of the form
>>> foo::f. This is slightly less efficient than a formal import and also loses
>>> the advantage of recording all dependencies in the NAMESPACE file, so this
>>> approach is usually not recommended. Evaluating foo::f will cause package
>>> foo to be loaded, but not attached, if it was not loaded already—this can
>>> be an advantage in delaying the loading of a rarely used package.
>>>
>>
>>
>> Would this be a better solution than importing when calling into a suggested
>> package?
>>
>> Davor
>>
>>
>> [[alternative HTML version deleted]]
>>
>>
>> ______________________________________________
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>>
>
>
>
> --
> Chief Scientist, RStudio
> http://had.co.nz/
>
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David Winsemius
Alameda, CA, USA
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