Bug #21106: The last iteration of the rb_ary_shuffle_bang function is useless

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-darwin21]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[usumerican (usumerican _)]

The number of iterations in the Fischer-Yates shuffle is (N-1) times.
In the following verification code, rand function is called N times.

class R
  def rand(n)
    puts n
    return 0
  end
end

a = [1,2,3,4,5,6,7,8,9,10]
puts a.shuffle(random: R.new).join(",")

The while conditional expression in the rb_ary_shuffle_bang function can be changed from while(n) to while(n > 1).

https://github.com/ruby/ruby/blob/db02a6b3ab4cabbdf492c26dcb1929b4ef0370a1/array.c#L6704

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset git|8dd0d63550c4da2ba7939f371f73825caa2e932e.

---

[Bug #21106] Remove the useless last iteration

When only one element remains, this simply swaps the first identical
element and has no actual effect.