R Under development (unstable) (2023-11-16 r85542 ucrt) -- "Unsuffered Consequences"
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> library("R.utils")
Loading required package: R.oo
Loading required package: R.methodsS3
R.methodsS3 v1.8.2 (2022-06-13 22:00:14 UTC) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.25.0 (2022-06-12 02:20:02 UTC) successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following object is masked from 'package:R.methodsS3':

    throw

The following objects are masked from 'package:methods':

    getClasses, getMethods

The following objects are masked from 'package:base':

    attach, detach, load, save

R.utils v2.12.3 successfully loaded. See ?R.utils for help.

Attaching package: 'R.utils'

The following object is masked from 'package:utils':

    timestamp

The following objects are masked from 'package:base':

    cat, commandArgs, getOption, isOpen, nullfile, parse, warnings

> 
> 
> # Reset seed
> if (exists(".Random.seed", envir=globalenv())) {
+   rm(list=".Random.seed", envir=globalenv())
+ }
> 
> # Generate a random number
> y0 <- runif(1)
> print(y0)
[1] 0.8878713
> 
> # Generate a random number using the same seed over and over
> yp <- NULL
> for (ii in 1:10) {
+   y <- withSeed({
+     runif(1)
+   }, seed=0x42)
+   print(y)
+   # Assert identical
+   if (!is.null(yp)) stopifnot(identical(y, yp))
+   yp <- y
+ }
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
[1] 0.9899366
> 
> # Generate a random number
> y <- runif(1)
> print(y)
[1] 0.3238957
> 
> 
> 
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> # Visibility
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> res <- withVisible({
+   withSeed({ 1 }, seed=42L)
+ })
> str(res)
List of 2
 $ value  : num 1
 $ visible: logi TRUE
> stopifnot(all.equal(res$value, 1))
> stopifnot(res$visible)
> 
> x <- 0
> res <- withVisible({
+   withSeed({ x <- 1 }, seed=42L)
+ })
> str(res)
List of 2
 $ value  : num 1
 $ visible: logi FALSE
> stopifnot(all.equal(res$value, 1))
> stopifnot(!res$visible)
> stopifnot(all.equal(x, 1))
> 
> 
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> # With RNG state reset
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> res <- withSeed(sample.int(100L, size=1L), seed=NULL)
> 
> 
> proc.time()
   user  system elapsed 
   0.37    0.14    0.50