R help - Feb 2014 - Package development: overriding a function from one package with a function from another?

Dear R users,

I am currently working on developing two packages, below is a simplified
version of my problem:

In package A I have some functions (say "sum_twice"), and I it calls
to
another function inside the package (say "slow_sum").
However, in package B, I wrote another function (say "fast_sum"), with
which I wish to replace the slow function in package A.

Now, how do I manage this "overriding" of the "slow_sum"
function with the
"fast_sum" function?

Here is a simplified example of such functions (just to illustrate):

############################

##############
# Functions in package A

slow_sum <- function(x) {
sum_x <- 0
for(i in seq_along(x)) sum_x <- sum_x + x[i]
 sum_x
}

sum_twice <- function(x) {
x2 <- rep(x,2)
slow_sum(x2)
}

##############
# A function in package B
fast_sum <- function(x) { sum(x) }

############################


If I only do something like:
slow_sum <- fast_sum
This would not work, since "sum_twice" uses "slow_sum" from
the NAMESPACE
of package A.

I tried using the following function when loading package "B":

assignInNamespace(x = "slow_sum", value = B:::fast_sum, ns =
"A")

This indeed works, however, it makes the CRAN checks return both a NOTE on
how I should not use ":::", and also a warning for using
assignInNamespace
(since it is supposed to not be very safe).



However, I am at a loss.
What would be a way to have "sum_twice" use "fast_sum"
instead of
"slow_sum"?


Thank you upfront for any feedback or suggestion,
With regards,
Tal



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