Question

I’m reading through Why’s Poignant Guide to Ruby and I came upon this code example wherein he adds a class variable and an instance method to the String class. The idea is that, given a string of an alien name, like “Paij-Ree”, we could run something like

"Paij-ree".determine_significance # returns "Personal AM"

Here is the code:

class String

  @@syllables = [
    { 'Paij' => 'Personal',
      'Gonk' => 'Business',
      'Blon' => 'Slave',
      'Stro' => 'Master',
      'Wert' => 'Father',
      'Onnn' => 'Mother' },
    { 'ree'  => 'AM',
      'plo'  => 'PM' }
  ]

  # a method to determine what a certain
  # name of his means

  def determine_significance

    parts = self.split( '-' )

    syllables = @@syllables.dup

    signif = parts.collect do |p|
      syllables.shift[p]
    end

    signif.join( ' ' )
  end

end

My question: What is going on in the collect block where there are square brackets after the Array#shift method? I’ve only been able to find examples where it is used like this:

letters = ['a','b','c']
letters.shift  # returns "a"

What’s going on here?

syllables.shift[p]

Answer 1

It’s doing exactly that. @@syllables is an array of hashes, so it shifts the first value out of the array, which is a hash. Then it accesses it using the split string as the key.

self.split( '-' ) returns a string array and that is mapped over with collect to replace it with the value in the hash.

The important part is that the array is duplicated to avoid destroying the original @@syllables so you can shift the duplicate.