[R] Files and classes in a package?

[Shin, Daehyok]

While installing my small package, I met a tricky problem.
For clarity, let me explain it with the following simplified example.

In ~/pkg/R/aclass.R,
    setClass("aclass", contains="bclass", representation(i="numeric"))

In ~/pkg/R/bclass.R,
    setClass("bclass", representation(j="numeric"))

After building a "pkg" package, the file pkg.R in R directory has:

    setClass("aclass", contains="bclass", representation(i="numeric"))
    setClass("bclass", representation(j="numeric"))

When combining the source files, R seems to generate one new source file
based on alphabetic orders of file names. In this case, loading the "pkg"
package failed with the following error message.

> library(pkg)
Error in methodsPackageMetaName("C", name) :
        The name of the object (e.g,. a class or generic function) to find
in the meta-data must be a single string (got an object of class "NULL")
> traceback()
12: methodsPackageMetaName("C", name)
11: classMetaName(Class)
10: getClassDef(Class, where)
9: getClass(cl, TRUE)
8: .validDataPartClass(clDef, name)
7: reconcilePropertiesAndPrototype(name, slots, prototype, superClasses,
       where)
6: makeClassRepresentation(Class, properties, superClasses, prototype,
       package, validity, access, version, sealed, where = where)
5: setClass("aclass", contains = "bclass", representation(i = "numeric"))
4: eval(expr, envir, enclos)
3: eval(i, envir)
2: sys.source(codeFile, loadenv, keep.source = keep.source)
1: library(pkg)

I suspect the reason is that class "bclass" is not defined when class
"aclass" is defined. To maintain source files effectively, I don’t want to
combine two files into one file or change their file names.

Surely, there may be elegant solutions for this somewhat trivial issue. But,
I can’t find it. Can you help me? Thanks.

Daehyok Shin