[R] How to get the namespace of a function?

[Fernando Saldanha]

I declared the environment of the function myfun to be NULL as follows:

environment(myfun) <- NULL

Later on I called that myfun and got an error message because the
function index() in the zoo package was called inside myfun and was
not visible:

Error in myfun(args) : couldn't find function "index"

I tried to use zoo::index() instead of index(), but that did not work.
In fact, zoo::index does not work even in the command line:

> z<-ts(1:5)
> z
Time Series:
Start = 1
End = 5
Frequency = 1
[1] 1 2 3 4 5
> index(z)
[1] 1 2 3 4 5
> zoo::index(z)
Error in loadNamespace(name) : package 'zoo' does not have a name space

How can I qualify index() so that it is visible inside the body of myfun?

Thanks for any suggestions,

FS