In accordance to the instructions on how to develop packages available under http://r-pkgs.had.co.nz/ and the devtools package, I put the R source files of my package in the folder R/.
If I need to call a function from another file in a particular file, then I need to call source("file_with_function.R") in this file.
After the package has been build (R CMD build my_package), then the call to source("file_with_function.R") is as far as I know no longer necessary.
Can I avoid the source() calls during development without getting error messages that objects/functions in other files don't exist?