Package developers,

I am trying to severely cut down on the number of dependencies of my package 
emmeans. It is now 48, which is quite a few (but that is down from over 100 in 
the preceding version, where I made the unwise choice of including a 
particularly greedy package in Imports). I hate to force users to install 
dozens of packages that they don't really need or want, but it seems very hard 
to avoid.

Case in point: emmeans provides additional methods for 'cld' and 'glht' from 
the multcomp package. Accordingly, I import their generics, and register my 
additional methods. But because I import the generics, I must list multcomp in 
Imports, and that results in the addition of 16 required packages, some of 
which I never use. More important, I believe that NONE of those 16 packages are 
required for the correct functioning of my courtesy methods. The only things I 
really need are the generics.

On the flip side, emmeans defines some generics of its own that I invite other 
package developers to extend so that emmeans supports their models. If those 
packages import emmeans, there is an overhead of 48 dependencies; again, most 
of these are packages that are not needed at all for those packages' methods to 
work. I don't like being responsible for that.

I believe this is a very common problem, not just with my own packages. It's 
one thing to extend a base method like 'print'; but extending methods in 
contributed packages creates these dependency explosions. I have hundreds of 
packages installed on my system - a couple dozen I care about, another few 
dozen that seem fairly desirable, and a couple hundred that I don't even know 
what they're for, other than that things will break if I uninstall them.

I do know of a couple ways to reduce these dependencies in the case of my 
multcomp dependencies:

1. I could simply export my S3 methods for cld and glht as functions, rather 
than registering them as S3 methods. 
    Then I could move multcomp to Suggests. The downside is that it clutters 
the namespace for emmeans.

2. I could define the generics for cld and glht in my own package, and export 
them; and move multcomp to Suggests.
    Again, it clutters the namespace, and creates warning messages about (if 
not real issues with) masking.

Probably (1) is better than (2), but is it better than what I do now? Is there 
something else that I (and probably a whole lot of other people) don't know?

I wish there were an ImportGenerics or an ImportWithoutDependencies or some 
such field possible in DESCRIPTION.

I appreciate any suggestions. Thanks


Russell V. Lenth  -  Professor Emeritus
Department of Statistics and Actuarial Science   
The University of Iowa  -  Iowa City, IA 52242  USA   
Voice (319)335-0712  -  FAX (319)335-3017  - 

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