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

From: Prof Brian Ripley <>
Date: Fri 03 Feb 2006 - 10:28:48 GMT

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 <>
>>>>>> 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, 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,        
Professor of Applied Statistics,
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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