source file in R package

Question

I'm building a very basic R package for my own use.

Some of the files need a function in another file.

So the R files try to source an R file. This fails during build. Neither

source("./util.R")

nor

source ("util.R")

work. R can't find the file.

All of the files are in the R directory of the package.

How do I call the file to make sure that it is found?

Thanks,

Answer 1

I think sourcing (source) is not required within a package since there must be kinda "lazy evaluation" (just parsing) of the objects you create that postpones the evaluation until you really call the functions of a package (which is a library = collection of functions that wait to be called from outside).

Hadley Wickham explains the background in his book R packages in the section "Top-level code".

To test this behaviour I have created a package using RStudio and added two files that call functions of the other file (like a circular reference):

File "f1.R":

f1 <- function() {
  print("f1")
  f2()
}

f4 <- function(a) {
  print(paste("f4:", a))
}

File "f2.R":

# f2.R
f2 <- function() {
  print("f2")
}

f3 <- function(a) {
  print(paste("f3:", a))
  f4(a)
}

RStudio creates a (source) package from this without problems.

I can also load the package, call the functions and the result is as expected:

> library(testpackage)
> testpackage:::f1()  # ::: allows calling a hidden function that was not exported. You could also create a NAMESPACE file instead
[1] "f1"
[1] "f2"
> testpackage:::f3("hello")
[1] "f3: hello"
[1] "f4: hello"
>

Summary: No source required in packages (until you want to test your code files without building a package before!).