[Rd] advise on Depends

[Paul Gilbert]

On 13-10-25 05:21 PM, Henrik Bengtsson wrote:
> On Fri, Oct 25, 2013 at 1:39 PM, John Chambers <jmc at r-project.org>
> wrote:
>> One additional point to Michael's summary:
>>
>> The "methods" package itself should stay in Depends:, to be safe.

It would be nice to have more detail about when this is necessary, 
rather than suggested as a general workaround. I thought the principle 
of putting things in Imports was that it is safer. I have methods listed 
in Imports rather than Depends in 16 of my packages, doing roughly what 
was the basis for the original question, and I am not aware of a 
problem, yet.

Paul

>>
>> There are a number of function calls to the methods package that
>> may be included in generated methods for user classes.  These have
>> not been revised to work when the methods package is not attached,
>> so importing the package only may run into problems.  This has been
>> an issue, for example, in using Rscript.
>
> To clarify that last sentence for those not aware (and hopefully
> spare someone having to troubleshoot this), executing R
> scripts/expressions using 'Rscript' rather than 'R' differs by which
> packages are attached by default.  Example:
>
> % Rscript -e "search()" [1] ".GlobalEnv"        "package:stats"
> "package:graphics" [4] "package:grDevices" "package:utils"
> "package:datasets" [7] "Autoloads"         "package:base"
>
> % R --quiet -e "search()"
>> search()
> [1] ".GlobalEnv"        "package:stats"     "package:graphics" [4]
> "package:grDevices" "package:utils"     "package:datasets" [7]
> "package:methods"   "Autoloads"         "package:base"
>
> Note how 'methods' is not attached when using Rscript.  This is
> explained in help("Rscript"), help("options"), and in 'R
> Installation and Administration'.
>
> /Henrik
>
>
>>
>> John
>>
>> On Oct 25, 2013, at 11:26 AM, Michael Lawrence
>> <lawrence.michael at gene.com> wrote:
>>
>>> On Wed, Oct 23, 2013 at 8:33 PM, Kasper Daniel Hansen <
>>> kasperdanielhansen at gmail.com> wrote:
>>>
>>>> This is about the new note
>>>>
>>>> Depends: includes the non-default packages: ‘BiocGenerics’
>>>> ‘Biobase’ ‘lattice’ ‘reshape’ ‘GenomicRanges’ ‘Biostrings’
>>>> ‘bumphunter’ Adding so many packages to the search path is
>>>> excessive and importing selectively is preferable.
>>>>
>>>> Let us say my package A either uses a class B (by producing an
>>>> object that has B embedded as a slot) from another package or
>>>> provides a specific method for a generic defined in another
>>>> package (both examples using S4). In both case my impression is
>>>> that best practices is I ought to Depend on such a package, so
>>>> it is a available at run time to the user.
>>>>
>>>>
>>> For classes, you just need to import the class with
>>> importClassesFrom(). For generics, as long as your package
>>> exports the method with exportMethods(), the generic will also be
>>> exported from your package, regardless of whether the defining
>>> package is attached. And the methods from the
>>> loaded-but-not-attached packages are available for the generic.
>>> So neither of these two is really a problem.
>>>
>>> The rationale for Depends is that the user might always want to
>>> use functions defined by another package with objects
>>> consumed/produced by your package, such as generics for which
>>> your package has not defined any methods. For example,
>>> rtracklayer Depends on GenomicRanges, because it imports objects
>>> from files as GenomicRanges objects.  So just consider what the
>>> user sees when looking at your API. What's private, what's
>>> public?
>>>
>>> Michael
>>>
>>>
>>>> Comments?
>>>>
>>>> Best, Kasper
>>>>
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>>>>
>>>>
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