How does Array#shuffle! works in ruby?

Ruby
1

Here I was trying to see how Array#shuffle! works with array objects. So
I started playing with it in my IRB:

[1,2,3]
#=> [1, 2, 3]
[1,2,3].shuffle!
#=> [3, 1, 2]

In the above code I understood how it works. And the below I was trying
to play with it more hard-way to see it from every corner.

[1,2,5]
#=> [1, 2, 5]
[1,2,5]<<[1,2,5]
#=> [1, 2, 5, [1, 2, 5]]

Till now I am good.

[1, 2, 5, [1, 2, 5]].shuffle!
#=> [5, 1, 2, [1, 2, 5]]

With above piece of code I have confusions. So below the questions came
in my head:

(a) Why shuffle! not worked recursively? As I expected that the

output of the inner array [1, 2, 5] also will be shuffled. But not
happened.

(b) Why does shuffle! not shuffle the element array [1, 2, 5] ,

rather works only with the 1, 2, 5, elements of the array [1, 2, 5, [1,
2, 5]] ? I thought the output would come as [[1, 2, 5],5, 1, 2]. So why
the element array didn’t change it’s position,rather the normal elements
did only?

Very interesting behavior it is showing:

a=[1,2,4]
#=> [1, 2, 4]
a<<[7,8]
#=> [1, 2, 4, [7, 8]]
a.shuffle!
#=> [[7, 8], 1, 4, 2]
a.shuffle!
#=> [4, 1, [7, 8], 2]
a.shuffle!
#=> [[7, 8], 2, 1, 4]
irb(main):006:0>

Does the shuffling really follow any order or its a random shuffling?

2

It’s random.

It’s behaving exactly the way it should, any recursion you should do
yourself. You wouldn’t like it if you had an array of objects and
shuffling the array messed with your objects’ internal state.

Why does shuffle! not shuffle the element array
#=> [1, 2, 4, [7, 8]]
a.shuffle!
#=> [[7, 8], 1, 4, 2]
You can see that the array inside the other array did, in fact, move.