how to use the regularized rf in ranger

library(ranger)
data("mtcars")

regularized_rf <- ranger(mpg ~ ., 
                         data = mtcars, 
                         num.trees = 500, 
                         # num.threads = 1, # needs to be set to 
                         # avoid parallelization
                         mtry = 7, 
                         importance = "impurity",
                         regularization.factor = 0.3)

standard_rf <- ranger(mpg ~ ., 
                      num.trees = 500,
                      data = mtcars, 
                      importance = "impurity",
                      mtry = 7)

# Prediction errors
regularized_rf$prediction.error
standard_rf$prediction.error

# Check variable importance
as.data.frame(importance(regularized_rf))
as.data.frame(importance(standard_rf))

# Number of variables used
length(unique(unlist(regularized_rf$forest$split.varIDs)))
length(unique(unlist(standard_rf$forest$split.varIDs)))