From: josefK <josefK@...>
Date: 2006-11-25T04:50:18+09:00
Subject: what is *self?

I encountered this added method to Array (I don't recall
the author - sorry ,)
It converts an Array to a Hash by providing a block to compute the
values given the array elements as keys:



class Array
   def to_h(&block)
     Hash[*self.collect{|v| [v,block.call(v)]}.flatten]
   end
end


#exp
a=[1,2,3]
h=a.to_h{|e| 2**e}
h.each{|k,v| puts "key=#{k} val=#{v}"}

#->key=1 val=2 key=2 val=4 key=3 val=8




Without the '*' on self it generates an error:
array2hash.rb:3:in `[]': odd number of arguments for Hash (ArgumentError)
         from array2hash.rb:3:in `to_h'
         from array2hash.rb:8


What does the '*' do to correct the error?

Does it push self up a level to Array somehow?

Does this notation generalize?



Thanks,

Mark