Question

Is there a no-op function in R so that, even if the parameters would be expensive to evaluate, it returns immediately? I’m looking for a conditional replacement of the stopifnot function.

> noop(runif(1e20))
# returns immediately and uses no memory

Answer 1

I think this would do:

noop <- function(...) invisible(NULL)

as lazy evaluation comes to the rescue here:

R> system.time(replicate(1e4, noop(runif(1e2))))
   user  system elapsed 
   0.01    0.00    0.01 
R> system.time(replicate(1e4, noop(runif(1e5))))
   user  system elapsed 
   0.01    0.00    0.02 
R> system.time(replicate(1e4, noop(runif(1e8))))
   user  system elapsed 
   0.01    0.00    0.01 
R> system.time(replicate(1e4, noop(runif(1e11))))
   user  system elapsed 
   0.01    0.00    0.01 
R> 

so even when we increase N no runtime increase can be seen.