Strange Ruby behavior

gistfile1.rb

# This example was run in IRB 1.9.2 p290.

# Initialize x, y, z, and t to some values using a parallel assignment:
> x, y, z, t = 1, 2, 3, 4
 => [1, 2, 3, 4]

# In the case above, '=' has lower precedence than ',', so there's a 4-ary
# lvalue and a 4-element rvalue.

> x, y = z, t = 1, 2
 => [3, 1, 2]
> [x, y, z, t]
 => [3, 1, 3, 1]

# More interesting is that this is different than what would have happened
# if I used parentheses around '=' to force right-associativity (which '='
# generally has anyway).

> x, y, z, t = 1, 2, 3, 4
 => [1, 2, 3, 4]

> x, y = (z, t = 1, 2)
 => [1, 2]
> [x, y, z, t]
 => [1, 2, 1, 2]