I like to read code. Often I take notes and it's a shame that I did never share them. But it's never to late to start.

So here are some notes on Ruby's set.rb. I hope you in turn share an interesting read with the world ;)

How to initialize a set

def initialize(enum = nil, &block)
  @hash ||= Hash.new

  enum.nil? and return

  if block
    do_with_enum(enum) { |o| add(block[o]) }
  else
    merge(enum)
  end
end

Ok much to notice here:

• A Set uses a hash internally to avoid duplicates
• Per default the merge method will just add() to the hash
• Interestingly enough you can pass a block to prepare the data

Some examples what this means:

Set.new
 => #<Set: {}>

 Set.new([1,2,2,3])
 => #<Set: {1, 2, 3}>

 Set.new(["ape", "APE", "aPe"]) { |val| val.downcase  }
 #<Set: {"ape"}>

A second possibility is hidden at the bottom of the file:

module Enumerable
  def to_set(klass = Set, *args, &block)
    klass.new(self, *args, &block)
  end
end

Some examples:

%w{hello, hello, you}.to_set
=> #<Set: {"hello,", "you"}>

 %w{hello, hello, world, "!"}.to_set {|val| val.upcase }
 => #<Set: {"HELLO,", "WORLD,", ""!""}>

Here is a third way:

def self.[](*ary)
  new(ary)
end

This is pretty nice trick. It produces a nice shortcut to create a set.

Set[1,2,3,4]
#<Set: {1, 2, 3, 4}>

Set arithmetic in set.rb

A nice feature of sets is, that they support set arithmetic. The implementation is pretty straightforward, this is one of the instances where Ruby's syntax really shines :)