introduce an equivalent function to achieve set.seed(NULL) in R 2.15.x

Author: yihui

R/globals.R

@@ -5,5 +5,5 @@
   # R's lazy-loading package scheme causes the private seed to be cached in the
   # package itself, making our PRNG completely deterministic. This line resets
   # the private seed during load.
-  withPrivateSeed(set.seed(NULL))
+  withPrivateSeed(reinitializeSeed())
 }

R/utils.R

@@ -84,6 +84,15 @@ withPrivateSeed <- function(expr) {
   )
 }
 
+# a homemade version of set.seed(NULL) for backward compatibility with R 2.15.x
+reinitializeSeed <- if (getRversion() >= '3.0.0') {
+  function() set.seed(NULL)
+} else function() {
+  if (exists('.Random.seed', globalenv()))
+    rm(list = '.Random.seed', pos = globalenv())
+  runif(1)  # generate any random numbers so R can reinitialize the seed
+}
+
 # Version of runif that runs with private seed
 p_runif <- function(...) {
   withPrivateSeed(runif(...))