What is dup?

ruby-talk
1

I am playing with an example in the ruby cookbook where a shuffle function is added to the array class:

class Array

   def shuffle!
     each_index do |i|
       j = rand(length-i) + i
       self[j], self[i] = self[i], self[j]
     end
   end

   def shuffle
     dup.shuffle!
   end

end

What I don't understand is the line "dup.shuffle!"

What is the dup object?

Dave.

2

dup returns a copy (duplicate) of the object. In the above code, it is
used to let you get back a shuffled copy of the Array, without
shuffling the original.

type:
ri Object#dup
for more info.

···

On 1/16/07, David Madden <moose56@gmail.com> wrote:

I am playing with an example in the ruby cookbook where a shuffle
function is added to the array class:

class Array

   def shuffle!
     each_index do |i|
       j = rand(length-i) + i
       self[j], self[i] = self[i], self[j]
     end
   end

   def shuffle
     dup.shuffle!
   end

end

What I don't understand is the line "dup.shuffle!"

What is the dup object?

3

> I am playing with an example in the ruby cookbook where a shuffle
> function is added to the array class:
>
> class Array
>
> def shuffle!
> each_index do |i|
> j = rand(length-i) + i
> self[j], self[i] = self[i], self[j]
> end
> end
>
> def shuffle
> dup.shuffle!
> end
>
> end
>
> What I don't understand is the line "dup.shuffle!"
>
> What is the dup object?
>

I think a wordier but equivalent way of doing that is:

return self.dup.shuffle!

That just means "duplicate myself, shuffle the duplicate, then return it."

···

On 1/16/07, Wilson Bilkovich <wilsonb@gmail.com> wrote:

On 1/16/07, David Madden <moose56@gmail.com> wrote:

4

dup returns a copy (duplicate) of the object. In the above code, it is
used to let you get back a shuffled copy of the Array, without
shuffling the original.

type:
ri Object#dup
for more info.

Thanks,

Dave.