Add random.sampleBuffer

changelog.md

@@ -124,6 +124,10 @@ with other backends. see #9125. Use `-d:nimLegacyJsRound` for previous behavior.
   (instead of skipping them sometimes as it was before).
 - Added optional `followSymlinks` argument to `setFilePermissions`.
 
+- Add `random.sampleBuffer` to in-place populate a `buffer` with random samples from `alphabet` arguments.
+  Can be used to generate random ASCII URL-Safe strings of specified length and chars.
+
+
 ## Language changes
 
 - `nimscript` now handles `except Exception as e`.

lib/pure/random.nim

@@ -656,4 +656,15 @@ when not defined(nimscript) and not defined(standalone):
       let now = times.getTime()
       randomize(convert(Seconds, Nanoseconds, now.toUnix) + now.nanosecond)
 
+proc sampleBuffer*[T](r: var Rand, buffer: var openArray[T]; alphabet: set[T]) {.inline, since: (1, 5).} =
+  ## Populates `buffer` with random samples from `alphabet`.
+  ## Can be used to generate random ASCII URL-Safe strings of specified length and chars.
+  # Inspired but not copied from Python 3.10 "secrets.token_urlsafe()".
+  runnableExamples:
+    import std/sugar
+    var r = initRand(666)
+    doAssert newString(8).dup(sampleBuffer(r, _, {'0'..'9'})).len == 8
+  for c in buffer.mitems: c = sample(r, alphabet)
+
+
 {.pop.}