From: "John W. Long" <ws@...>
Date: 2003-07-19T12:20:39+09:00
Subject: Ruby Golf: Object Diff

The problem:

When debugging a program that uses large objects and a test fails because
the object is different from the expected it is sometimes hard to discern
the difference between the objects from the output of Test::Unit.

The goal of this hole is to create a method that will output the differences
of two objects in an intelligent manner. Something similar in concept to
this:
        #<TestObject1:0x1 ... @b="b", ... @d="d", ...>
        #<TestObject1:0x2 ... @b="", ... @d="", ...>

You are free to use whatever method you might choose. Program size does not
matter. Creativity and one-up-man-ship is encouraged. We will probably post
the best solution on the wiki.

The following test case is a guideline and may be changed if you have better
ideas for how such a method should work:

<TestCase>
class TestObject1
 attr_accessor :a, :b, :c, :d, :e
 def initialize(a, b, c, d, e = nil)
  @a, @b, @c, @d, @e = a, b, c, d, e
 end
end
class TestObject2
 attr_accessor :a, :b, :c, :d, :f, :g
 def initialize(a, b, c, d, f, g)
  @a, @b, @c, @d, @f, @g = a, b, c, d, f, g
 end
end

class TC_ObjectDiff < Test::Unit::TestCase
 def test_to_s
  object = TestObject1.new('a', 'b', 'c', 'd', [1, 2, 3, 4])
  def object.__id__
   0
  end
  assert_equal('#<TestObject1:0x0 @a="a", @b="b", @c="c", @d="d", @e=[1, 2,
3, 4]>',
   ObjectDiff.object_to_s(object))
 end
 def test_compare
  object1 = TestObject1.new('a', 'b', 'c', 'd')
  def object1.__id__
   1
  end
  object2 = TestObject1.new('a', '', 'c', '')
  def object2.__id__
   2
  end
  string1, string2 = ObjectDiff.compare(object1, object2)
  puts [string1, string2]
  assert_equal('#<TestObject1:0x1 ... @b="b", ... @d="d", ...>', string1)
  assert_equal('#<TestObject1:0x2 ... @b="", ... @d="", ...>', string2)

  complexObject1 = TestObject1.new('1', {:a => 1, :b => 2, :j => 3}, [1, 2,
3], object1)
  def complexObject1.__id__
   3
  end
  complexObject2 = TestObject1.new('1', {:a => 2, :b => object1, :j => 3},
[0, 2], object2)
  def complexObject2.__id__
   4
  end
  string1, string2 = ObjectDiff.compare(complexObject1, complexObject2)
  puts [string1, string2]
  assert_equal('#<TestObject1:0x3 ... @b={:a=>1, :b=>2, ...}, @c=[1, ... 3],
@d=#<TestObject1:0x1 ... @b="b", ... @d="d", ...>, ...>', string1)
  assert_equal('#<TestObject1:0x4 ... @b={:a=>2, :b=>#<TestObject1:0x284a3a8
@c="c", @b="b", @e=nil, @a="a", @d="d">, ...}, @c=[0, ...],
@d=#<TestObject1:0x2 ... @b="", ... @d="", ...>, ...>', string2)
 end
 def test_compare_different_classes
  object1 = TestObject1.new('a', 'b', 'c', 'd')
  def object1.__id__
   5
  end
  object2 = TestObject2.new('a', '', 'c', '', 'f', 'g')
  def object2.__id__
   6
  end

  string1, string2 = ObjectDiff.compare(object1, object2)
  puts [string1, string2]
  assert_equal('#<TestObject1:0x5 ... @b="b", ... @d="d", @e=nil>', string1)
  assert_equal('#<TestObject2:0x6 ... @b="", ... @d="", @f="f", @g="g">',
string2)
 end
 def test_compare_array
  a = [1, 2, 3, 4, 5]
  b = [1, 3, 4, 4, 5, 6]
  string_a, string_b = ObjectDiff.compare_array(a, b)
  puts [string_a, string_b]
  assert_equal('[... 2, 3, ... ...]', string_a)
  assert_equal('[... 3, 4, ... ... 6]', string_b)
 end
 def test_compare_hash
  a = {
   :a => 1,
   :b => 2,
   :c => 3,
   :d => 4
  }
  b = {
   :j => 2,
   :b => 3,
   :c => 3,
   :d => 5
  }
  string_a, string_b = ObjectDiff.compare_hash(a, b)
  puts [string_a, string_b]
  assert_equal('{:a=>1, :b=>2, ... :d=>4}', string_a)
  assert_equal('{       :b=>3, ... :d=>5, :j=>2}', string_b)
 end
end
</TestCase>



Here is my solution:



<MySolution>
class ObjectDiff
 class Node
  attr_reader :object, :nodes

  def initialize(value)
   @object = value
   @nodes = {}
   variables = @object.instance_variables
   variables.each { |key|
    variable = @object.instance_eval(key)
    @nodes[key] = Node.new(variable)
   }
  end

  def to_s
   return @object.inspect if [String, Integer, NilClass, Array, Hash,
Fixnum, Integer, Bignum].index(@object.class)
   string = s_begin(self)
   @nodes.each { |key, node|
    string << "#{key}=#{node.to_s}, "
   }
   s_end(string)
  end

  def compare_with(node)
   return ::ObjectDiff::compare_hash(@object, node.object) if
@object.instance_of?(Hash) and node.object.instance_of?(Hash)
   return ::ObjectDiff::compare_array(@object, node.object) if
@object.instance_of?(Array) and node.object.instance_of?(Array)
   return [@object.inspect, node.object.inspect] if [String, Integer,
NilClass, Array, Hash, Fixnum, Integer, Bignum].index(@object.class)

   keys = []
   @nodes.each_key { |key|
    keys << key
   }
   node.nodes.each_key { |key|
    keys << key
   }
   keys.uniq!
   keys.sort!

   string1 = s_begin(self)
   string2 = s_begin(node)

   keys.each { |key|
    node1 = @nodes[key]
    node2 = node.nodes[key]
    if @nodes.has_key?(key) and node.nodes.has_key?(key)
     if node1.to_s == node2.to_s
      string1 << '... '
      string2 << '... '
     else
      s1, s2 = node1.compare_with(node2)
      string1 << "#{key}=#{s1}, "
      string2 << "#{key}=#{s2}, "
     end
    else
     if @nodes.has_key?(key)
      string1 << "#{key}=#{node1.to_s}, "
     end
     if node.nodes.has_key?(key)
      string2 << "#{key}=#{node2.to_s}, "
     end
    end
   }

   string1 = s_end(string1)
   string2 = s_end(string2)

   [string1, string2]
  end

  def s_begin(node)
   "#<#{node.object.class.name}:0x#{format('%x', node.object.__id__)} "
  end

  def s_end(string)
   string.chomp!(' ')
   string.chomp!(',')
   string << '>'
  end
 end

 def self.object_to_s(object)
  Node.new(object).to_s
 end

 def self.compare(object1, object2)
  node1 = Node.new(object1)
  node2 = Node.new(object2)
  node1.compare_with(node2)
 end

 def self.compare_array(array1, array2)
  if array1.size < array2.size
   a = array2
   b = array1
   flipped = true
  else
   a = array1
   b = array2
   flipped = false
  end

  string1 = '['
  string2 = '['

  for i in 0...a.size
   if i < b.size
    node1 = Node.new(a[i])
    node2 = Node.new(b[i])
    if node1.to_s == node2.to_s
     string1 << '... '
     string2 << '... '
    else
     string_a, string_b = compare(a[i], b[i])
     string1 << "#{string_a}, "
     string2 << "#{string_b}, "
    end
   else
    string1 << Node.new(a[i]).to_s
   end
  end

  string1.strip!
  string1.chomp!(',')
  string2.strip!
  string2.chomp!(',')

  string1 << ']'
  string2 << ']'

  if flipped
   [string2, string1]
  else
   [string1, string2]
  end
 end

 def self.compare_hash(hash1, hash2)
  keys = []
  hash1.each_key { |key|
   keys << key
  }
  hash2.each_key { |key|
   keys << key
  }
  keys.uniq!
  keys.sort!{ |a, b|
   a = a.inspect if a.is_a?(Symbol)
   b = b.inspect if b.is_a?(Symbol)
   a <=> b
  }

  string1 = '{'
  string2 = '{'

  keys.each { |key|
   node1 = Node.new(hash1[key])
   node2 = Node.new(hash2[key])
   if hash1.has_key?(key) and hash2.has_key?(key)
    if node1.to_s == node2.to_s
     string1 << '... '
     string2 << '... '
    else
     s1, s2 = node1.compare_with(node2)
     string1 << "#{key.inspect}=>#{s1}, "
     string2 << "#{key.inspect}=>#{s2}, "
    end
   else
    if hash1.has_key?(key) and not hash2.has_key?(key)
        append = "#{key.inspect}=>#{node1.to_s}, "
     string1 << append
     string2 << (' ' * append.size)
    else
     append = "#{key.inspect}=>#{node2.to_s}, "
     string2 << append
     string1 << (' ' * append.size)
    end
   end
  }
  string1.strip!
  string1.chomp!(',')
  string2.strip!
  string2.chomp!(',')

  string1 << '}'
  string2 << '}'

  [string1, string2]
 end
end
</MySolution>



Feel free to improve upon my code or create your own. Remember this is for
posterity, so be honest...

___________________
John Long
www.wiseheartdesign.com