What does this mean in Ruby language?

Question

Run the following code,

a = [1, 2, 3, 4, 5]
head, *tail = a
p head
p tail

You will get the result

1
[2, 3, 4, 5]
         


        

Answer 1

First, it is a parallel assignment. In ruby you can write

a,b = 1,2

and a will be 1 and b will be 2. You can also use

a,b = b,a

to swap values (without the typical temp-variable needed in other languages).

The star * is the pack/unpack operator. Writing

a,b = [1,2,3]

would assign 1 to a and 2 to b. By using the star, the values 2,3 are packed into an array and assigned to b:

a,*b = [1,2,3]