From: Steve Tuckner <SAT@...>
Date: 2001-04-18T00:09:11+09:00
Subject: [ruby-talk:13759] Odd Hash Behavior (long)

Could someone explain the following behavior?
 
The following code
-------------------------------
class A
  attr_reader :value
  def initialize
    @value = 0
  end
  def add_one
    @value += 1
  end
end
 
aTestHash = Hash.new(A.new)
 
aTestHash['A'] = A.new
aTestHash['A'].add_one
aTestHash['B'].add_one
print "aTestHash['A'] = #{aTestHash['A'].value}\n"
print "aTestHash['B'] = #{aTestHash['B'].value}\n"
 
print "\nAll Hash values:\n"
aTestHash.each { |aKey, aA| print "#{aKey} = #{aA.value}\n" }
-------------------------------
 
produces the following output
 
-------------------------------
aTestHash['A'] = 1
aTestHash['B'] = 1
 
All Hash values:
A = 1
-------------------------------
 
I have made this work by testing for key existence and adding the new entry
manually like the following
 
if !aTestHash.has_key?(index) then
  aTestHash[index] = A.new
end
aTestHash[index].add_one
 
Why doesn't the method above work as expected (why no B in the hash?) and is
there a consise way to do this that I don't know about.
 
Thanks,
 
Steve Tuckner