From: Tom Willis <tom.willis@...>
Date: 2005-03-07T02:30:33+09:00
Subject: Noob:Objects as key in hash

Hi all,

I didn't want my first bit of participation on this list to be
something this silly. But I'm afraid I missed something vital in my 48
hour crash course.

If someone could take 10 seconds and tell me what I'm doing wrong I'd
greatly appreciate it and will give you props in my epitaph.

Feel free to point out and make fun of the style too :) I have thick skin.

I want to use an object as a key in a Hash. 


here's some example code...

def main
  puts "running this script..."
  testpointid
end

def testpointid
  p = PointID.new(1,1)
  p2 = PointID.new(1,2)
  pdup = PointID.new(1,1)
  print "p!=pdup\n" if p!=pdup
  d = Hash.new()
  d[p]="point1"
  d[p2]="point2"

  #both of these return nil and I don't understand why
  print "PointID test failed" if d[p]!="point1"
  print "PointID test failed" if d[pdup]!="point1" 

  #this works, but it's not quite the interface I want 
  d[p.hash]="point1"
  d[p2.hash]="point2"

  
  print "PointID test failed" if d[p.hash]!="point1"
  print "PointID test failed" if d[pdup.hash]!="point1" 


end

class PointID
  attr_reader :x,:y

  def initialize(x,y)
    @x = x
    @y = y
    @x.freeze
    @y.freeze

  end

  def hash
    return [@x.object_id,@y.object_id].to_s
  end

  def ==(other)
    return hash == other.hash
  end 

  def to_s
    return hash()
  end

end

-- 
Thomas G. Willis
http://paperbackmusic.net