How do I re-register S3 method inside R package?

Question

I am working on a tool for R and I can't figure out how to replace S3 methods inside packages. Let's take print.aov for example. I want to replace its body, but inside stats namespace. If I just reassign the function in the namespace

> reassignInEnv <- function(name, obj, env) {
    if (exists(name, env)) {
        if (bindingIsLocked(name, env)) {
            unlockBinding(name, env)
            assign(name, obj, envir = env)
            lockBinding(name, env)
        } else {
            assign(name, obj, envir = env)
        }
    } else {
        stop("Object does not exist")
    }
}
> reassignInEnv("print.aov", function(x, ...) { print("replaced function!") }, env = getNamespace('stats'))

Previously registered function will be called when print dispatches, instead of a new one.

> print(aov(yield ~ block + N * P + K, npk))
Call:
   aov(formula = yield ~ block + N * P + K, data = npk)

Terms:
                   block        N        P        K      N:P Residuals
Sum of Squares  343.2950 189.2817   8.4017  95.2017  21.2817  218.9033
Deg. of Freedom        5        1        1        1        1        14

Residual standard error: 3.954232
Estimated effects may be unbalanced

I also tried R.methodsS3 package, but it won't work, because it tries to do an assignment in a locked environment.

> unlockBinding("print.aov", getNamespace('stats'))
> setMethodS3(name = "print", definition = function(x, ...) { print("replaced function!") }, class = "aov", private = TRUE, export = FALSE, envir = getNamespace('stats'))
Error in eval(expr, envir, enclos) : 
  cannot add bindings to a locked environment

How can make sure the new function is called when S3 method dispatch occurs?

Answer 1

Have you tried assignInNamespace()?

printAOV <- function(x, ...) print("replaced function!")
assignInNamespace("print.aov", printAOV, ns = asNamespace("stats"))

print(aov(yield ~ block + N * P + K, npk))
# [1] "replaced function!"