Calling a function from a namespace

Question

I'm trying to alter the functionality of a few commands in a package in R. It's easy enough to see the source of the commands. However the function calls other functions that are in the package namespace. These functions are not exported objects. So how can I access them?

Specific example:

How would I access the asCall() function that is used in copula::rmvdc?

require(copula)
copula::rmvdc
getAnywhere("asCall")

so as.Call() exists in the copula package, but how do I access it?

> copula::asCall
Error: 'asCall' is not an exported object from 'namespace:copula'

Solution 1

Try this:

copula:::asCall

This was previously answered on R-help. That function was not exported in the package namespace, so you need to use the ::: operator instead. Typically functions are not exported when they are not intended for general usage (e.g. you don't need to document them in this case).

Solution 2

When developing, ?assignInNamespace is very useful.

This allows you to inject a new copy of a non-exported function into a package's namespace.

It would be nice if R's error message was more helpful. Instead of:

Error: 'matrixToPaths' is not an exported object from 'namespace:OpenMx'

Why not add:

You might try OpenMx:::matrixToPaths"