[R-pkg-devel] Checking package dependencies before loading namespace

[Tiago Olivoto]

Dear all,
I have a package called pliman <https://CRAN.R-project.org/package=pliman>
which depends on the Bioconductor package EBImage.

When running install.packages("pliman") I get the following warning

Warning in install.packages :  dependency ‘EBImage’ is not available

and thus when loading the package with library(pliman), the following error
occurs

Erro: package or namespace load failed for ‘pliman’ in loadNamespace(i,
c(lib.loc, .libPaths()), versionCheck = vI[[i]]):
 there is no package called ‘EBImage’

I created a check function to check if EBImage is available and if not, ask
users if they want to install it

---
check_ebi <- function(){
  if(!requireNamespace("EBImage", quietly = TRUE)) {
    inst <-
    switch(menu(c("Yes", "No"), title = "Package {EBImage} required but not
available.\nDo you want to install it now?"),
           "yes", "no")
    if(inst == "yes"){
      if (!requireNamespace("BiocManager", quietly = TRUE)){
        install.packages("BiocManager")
      }
      BiocManager::install("EBImage", ask = FALSE, update = FALSE)
    } else{
      message("To use {pliman}, first install {EBImage} with
'BiocManager::install(\"EBImage\")'.")
    }
  }
}
---

Is there any way to run this function prior to namespace loading? I tried
putting check_ebi() into .onLoad() but the same error occurs.

Thanks in advance for any suggestions.
Tiago

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