[Bioc-devel] [devteam-bioc] Use Imports instead of Depends in the DESCRIPTION files of bioconductor packages.

Peng Yu pengyu.ut at gmail.com
Wed Dec 31 17:47:06 CET 2014

On Wed, Dec 31, 2014 at 9:41 AM, Martin Morgan <mtmorgan at fredhutch.org> wrote:
> On 12/24/2014 07:31 PM, Maintainer wrote:
>> Hi,
>> Many bioconductor packages Depends on other packages but not Imports
>> other packages. (e.g., IRanges Depends on BiocGenerics.) Imports is
>> usually preferred to Depends.
>> http://stackoverflow.com/questions/8637993/better-explanation-of-when-to-use-imports-depends
>> http://obeautifulcode.com/R/How-R-Searches-And-Finds-Stuff/
>> Could the unnecessary Depends be forced to be replaced by Imports?
>> This should improve the package load time significantly.
> R package symbols and other objects are collated at build time into a 'name
> space'. When used,
> - Import: loads the name space from disk.
> - Depends: loads the name space from disk, and attaches it to the search()
> path.
> Attaching is very inexpensive compared to loading, so there is no speed
> improvement gained by Import'ing instead of Depend'ing.

Yes. For example, changing Depends to Imports does not improve the
package load time much.

But loading a package in 4 sec seems to be too long.

>  system.time(suppressPackageStartupMessages(library(MBASED)))
   user  system elapsed
  4.404   0.100   4.553

For example, it only takes 10% of the time to load ggplot2. It seems
that many bioconductor packages have similar problems.

> system.time(suppressPackageStartupMessages(library(ggplot2)))
   user  system elapsed
  0.394   0.036   0.460

> The main reason to Depend: on a package is because the symbols defined by
> the package are needed by the end-user. Import'ing a package is appropriate
> when the package provides functionality only relevant to the package author.

What causes the load time to be too long? Is it because exporting too
many functions from all dependent packages to the global namespace?

> There are likely to be specific packages that mis-use Depends; packages such
> as IRanges, GenomicRanges, etc use Depends: as intended, to  provide
> functions that are useful to the end user.
> Maintainers are certainly encouraged to think carefully about adding
> packages providing functionality irrelevant to the end-user to the Depends:
> field. The codetoolsBioC package (available from svn, see
> http://bioconductor.org/developers/how-to/source-control/) provides some
> mostly reliable hints to package authors about correctly formulating a
> NAMESPACE file to facilitate using Imports: instead of Depends:.
> General questions about Bioconductor packages should be addressed to the
> support forum https://support.bioconductor.org.
> Questions about Bioconductor development (such as this) should be addressed
> to the bioc-devel mailing list (subscription required)
> https://stat.ethz.ch/mailman/listinfo/bioc-devel.
> I have cc'd the bioc-devel mailing list; I hope that is ok.


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