[Rd] Namespace dependency not required

[Uwe Ligges]

On 18.03.2012 16:08, Patrick Giraudoux wrote:
> Le 18/03/2012 14:57, Uwe Ligges a écrit :
>>
>>
>> On 18.03.2012 11:21, Patrick Giraudoux wrote:
>>> Hi,
>>>
>>> I am working at adding namespace to my packages, carefully following the
>>> doc "Writing R extensions" and some threads on the web. However I cannot
>>> find clear explanation about how to best deal with the import or
>>> importFrom functions in the name space. To make it short:
>>>
>>> To declare dependencies in the description file either after Depends:
>>> (packages including functions that are called from a package function)
>>> or after Suggests: (packages that are called eg from the doucmentation
>>> examples), works well. In this case one does not need to declare import
>>> in the namespace file.
>>>
>>> However, declaring dependencies sometimes for using only one function in
>>> a given package looks a bit over the top, and I though I could use
>>> importFrom in the namespace to deal with that. So removing the
>>> corresponding declaration in Depends (description file) and declaring
>>> eg importFrom(splancs, inout) in the namespace always led to:
>>>
>>> * checking package dependencies ... ERROR
>>> Namespace dependency not required: 'splancs'
>>>
>>> Same thing with import(sp). I have the same trouble if I do not remove
>>> the declarations in Depends.
>>>
>>> So, I can hardly follow the meaning of the "Writing R extension" doc:
>>>
>>> Packages implicitly import the base namespace. Variables exported from
>>> other packages with namespaces need to be imported explicitly using the
>>> directives |import| and |importFrom|. The |import| directive imports all
>>> exported variables from the specified package(s). Thus the directives
>>>
>>> import(foo, bar)
>>>
>>> specifies that all exported variables in the packages *foo* and *bar*
>>> are to be imported. If only some of the exported variables from a
>>> package are needed, then they can be imported using |importFrom|. The
>>> directive
>>>
>>> importFrom(foo, f, g)
>>>
>>> specifies that the exported variables |f| and |g| of the package *foo*
>>> are to be imported.
>>>
>>> Can anybody tell us the conditions for which import and importFrom
>>> commands should be used in the NAMESPACE rather than in the Depends and
>>> Suggests declarations of the description file, and the conditions of
>>> their applicability (without error message... eg with a working
>>> example) ?
>>
>> If you import from another namespace (which is the recommended way
>> rather than just relying on search order), do not forget to declare it
>> as "Imports" in your DESCRIPTION file. Your package depends on the
>> other one: It could not be loaded without having the other one
>> installed now.
>>
>> Uwe Ligges
>>
>
> OK. got it (more or less).
>
> With this in the description file:
>
> Depends: boot (>= 1.3-4), nlme(>= 3.1-64), rgdal (>= 0.7-8), sp (>=
> 0.9-97), spdep (>= 0.5-43), splancs (>= 2.01-31)
>
> importFrom(splancs, inout) is accepted in the NAMESPACE file and I have
> no error message with rcmd check.
>
> Irr works also with:
>
> Depends: boot (>= 1.3-4), nlme(>= 3.1-64), rgdal (>= 0.7-8), sp (>=
> 0.9-97), spdep (>= 0.5-43)
> Imports: splancs (>= 2.01-31)
>
> Practically, I a am safe (thanks a lot), but I am however still hungry
> to learn a bit more. I hardly understand what R does when reading the
> suggests and imports in the DESCRIPTION file compared to what it does
> reading the NAMESPACE (my mistake was to believe that one was a
> substitute for the other). From a practical point of view, why is it
> important to use import or importFrom in the NAMESPACE when everything
> looks like working well when declarations are done in the DESCRIPTION
> file only (eg in depends or imports)? It is not crystal clear to me even
> reading carefully "Writing R extension". DESCRIPTION file is used to get
> the "list of packages that will be attached (...) before the current
> package" (indeed, now, I no longer needs to use 'require' within my
> package functions). In simple words, what may add the NAMESPACE to that ?
>
> Apologize to be so poorly aware (= so much stupid) about the role of
> each of those declaration spaces.

Please read some literature about NAMESPACES, e.g. documentation in 
Writing R Extensions plus Luke Tierney's articles in R News.

A NAMESPACE import imports functionality of another namespace into your 
own namespace and hence avoids problems caused by name clashes.
The DESCRIPTION file is required to derive dependency structure of 
packages, i.e. derive which package has to be *installed* first etc.

Uwe Ligges





>
> Best,
>
> Patrick
>
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