Why does the expression "a, b = 5" set a to 5, but b to nil in Ruby?

Question

(irb) a, b = 5
a => 5
b => nil

Shouldn't that be the other way around? What is actually happening here?

Answer 1

As I was writing this my coworker discovered why:

Ruby treats a, b = 5 as a, b = 5, nil

In Python3, a TypeError is thrown.

Answer 2

In order to assign a value to b using multiple assignment you'd have to give it a second value.

a, b = 5, 6

a = 5
b = 6

When you don't supply a second value, Ruby gives b a value of nil