[Rd] SaveImage, LazyLoad, S4 and all that {was "install.R ... files"}

Prof Brian Ripley ripley at stats.ox.ac.uk
Fri Feb 3 11:28:48 CET 2006

The short answer is that there are no known (i.e. documented) differences, 
and no examples on CRAN which do not work with lazy-loading (except party, 
which loads the saved image in a test).  And that includes examples of 
packages which share S4 classes.  But my question was to tease things like 
this out.

You do need either SaveImage or LazyLoad in a package that defines S4 
classes and methods, since SetClass etc break the `rules' for R files in 
packages in `Writing R Extensions'.

When I have time I will take a closer look at this example.

On Fri, 3 Feb 2006, Martin Maechler wrote:

>>>>>> "Seth" == Seth Falcon <sfalcon at fhcrc.org>
>>>>>>     on Thu, 02 Feb 2006 11:32:42 -0800 writes:
>    Seth> Thanks for the explaination of LazyLoad, that's very helpful.
>    Seth> On  1 Feb 2006, ripley at stats.ox.ac.uk wrote:
>    >> There is no intention to withdraw SaveImage: yes.  Rather, if
>    >> lazy-loading is not doing a complete job, we could see if it could
>    >> be improved.
>    Seth> It seems to me that LazyLoad does something different with respect to
>    Seth> packages listed in Depends and/or how it interacts with namespaces.
>    Seth> I'm testing using the Bioconductor package graph and find that if I
>    Seth> change SaveImage to LazyLoad I get the following:
> Interesting.
> I had also the vague feeling that  saveImage  was said to be
> important when using  S4 classes and methods; particularly when
> some methods are for generics from a different package/Namespace
> and other methods for `base' classes (or other classes defined
> elsewhere).
> This is the case of 'Matrix', my primary experience here.
> OTOH, we now only use 'LazyLoad: yes' , not (any more?)
> 'SaveImage: yes' -- and honestly I don't know / remember why.
> Martin
>    Seth> ** preparing package for lazy loading
>    Seth> Error in makeClassRepresentation(Class, properties, superClasses, prototype,  :
>    Seth> couldn't find function "getuuid"
>    Seth> Looking at the NAMESPACE for the graph package, it looks like it is
>    Seth> missing some imports.  I added lines:
>    Seth> import(Ruuid)
>    Seth> exportClasses(Ruuid)
>    Seth> Aside: am I correct in my reading of the extension manual that if one
>    Seth> uses S4 classes from another package with a namespace, one
>    Seth> must import the classes and *also* export them?
>    Seth> Now I see this:
>    Seth> ** preparing package for lazy loading
>    Seth> Error in getClass("Ruuid") : "Ruuid" is not a defined class
>    Seth> Error: unable to load R code in package 'graph'
>    Seth> Execution halted
>    Seth> But Ruuid _is_ defined and exported in the Ruuid package.
>    Seth> Is there a known difference in how dependencies and imports are
>    Seth> handled with LazyLoad as opposed to SaveImage?
>    Seth> Thanks,
>    Seth> + seth

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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