Fun with the asterisk.rb

The interesting world of the asterisk in Ruby:

Of course we can multiply with it and it's quite handy in a regex, but there are two other interesting uses.

First, variable arguments in the method signature:

def hmm(*args)
  first, *rest = *args
  puts first.inspect
  puts rest.inspect
end

So we can pass any number of things:

>> hmm(1,2,3,4,5,6)
1
[2, 3, 4, 5, 6]

>> hmm([1,3,4],4,5,6)
[1, 3, 4]
[4, 5, 6]

We can see another use of the asterisk in this method here:
first, *rest = *args

The first argument is assigned to the variable "first" and everything else is globbed together into an array, assigned to "rest".


BUT....

There is another awesome yet mysterious use of our beloved asterisk.  It can be used to convert an array into the raw form of it's elements, essentially unwrapping its contents.

For example:
>> a, b, c = *[:a, :b, :c]
=> [:a, :b, :c]
>> puts a.inspect
:a
>> puts b.inspect
:b
>> puts c.inspect
:c

This is equivalent to:
>> a, b, c = :a, :b, :c

Now lets use that in a method call:
>> array = [:a, :b, :c]
=> [:a, :b, :c]
>> hmm(*array)
:a
[:b, :c]

We can even mix "regular" arguments with it:
>> hmm("awesome", *array)
"awesome"
[:a, :b, :c]

Sweet!  Now let's add stuff to that array in the same expression:
>> hmm(*array + [:d, :e, :f])
:a
[:b, :c, :d, :e, :f]
=> nil


Let's add an argument *after* that array expansion!
>> hmm(*array, "oh snap")
SyntaxError: compile error
(irb):22: syntax error, unexpected tSTRING_BEG, expecting tAMPER
hmm(*array, "oh snap")
             ^
(irb):22: syntax error, unexpected ')', expecting $end
	from (irb):22

OH SNAP!

It would seem that this "convert an array to a raw list of its elements" usage of our beloved asterisk does something extra.  

What is it doing?  Where is this implemented in the interpreter?  What is this usage of the asterisk actually called?