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2010-11-08T14:26:57.517
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A year ago <a href="http://alicebobandmallory.com/articles/2009/11/02/comparing-instance-variables-in-ruby" rel="nofollow">I monkey patched</a> a kind of cryptic <code>instance_variables_compare</code> on <code>Object</code>. I guess you could use that. <pre><code>class Object def instance_variables_compare(o) Hash[*self.instance_variables.map {|v| self.instance_variable_get(v)!=o.instance_variable_get(v) ? [v,o.instance_variable_get(v)] : []}.flatten] end end </code></pre> A cheesy example <pre><code>require 'Date' class Cheese attr_accessor :name, :weight, :expire_date def initialize(name, weight, expire_date) @name, @weight, @expire_date = name, weight, expire_date end end stilton=Cheese.new('Stilton', 250, Date.parse("2010-12-02")) gorgonzola=Cheese.new('Gorgonzola', 250, Date.parse("2010-12-17")) </code></pre> irb is my weapon of choice <pre><code>>> stilton.instance_variables_compare(gorgonzola) => {"@name"=>"Gorgonzola", "@expire_date"=>#<Date: 4910305/2,0,2299161>} >> gorgonzola.instance_variables_compare(stilton) => {"@name"=>"Stilton", "@expire_date"=>#<Date: 4910275/2,0,2299161>} >> stilton.expire_date=gorgonzola.expire_date => #<Date: 4910305/2,0,2299161> >> stilton.instance_variables_compare(gorgonzola) => {"@name"=>"Gorgonzola"} >> stilton.instance_variables_compare(stilton) => {} </code></pre> As you can see the <code>instance_variables_compare</code> returns an empty Hash if the two objects has the same content. An array of cheese <pre><code>stilton2=Cheese.new('Stilton', 210, Date.parse("2010-12-02")) gorgonzola2=Cheese.new('Gorgonzola', 250, Date.parse("2010-12-17")) arr=[]<<stilton<<stilton2<<gorgonzola<<gorgonzola2 </code></pre> One hash without problems and one with <pre><code>h={} problems=Hash.new([]) arr.each {|c| if h.has_key?(c.name) if problems.has_key?(c.name) problems[c.name]=problems[c.name]<<c elsif h[c.name].instance_variables_compare(c) != {} problems[c.name]=problems[c.name]<<c<<h[c.name] h.delete(c.name) end else h[c.name]=c end } </code></pre> Now the Hash <code>h</code> contains the objects without merging problems and the <code>problems</code> hash contains those that has instance variables that differs. <pre><code>>> h => {"Gorgonzola"=>#<Cheese:0xb375e8 @name="Gorgonzola", @weight=250, @expire_date=#<Date: 2010-12-17 (4911095/2,0,2299161)>>} >> problems => {"Stilton"=>[#<Cheese:0xf54c30 @name="Stilton", @weight=210, @expire_date=#<Date: 2010-12-02 (4911065/2,0,2299161)>>, #<Cheese:0xfdeca8 @name="Stilton", @weight=250,@expire_date=#<Date: 2010-12-02 (4911065/2,0,2299161)>>]} </code></pre> As far as I can see you will not have to modify this code at all to support an array of <code>UserInfo</code> objects. It would most probably be much faster to compare the properties directly or with a override of <code>==</code>. This is how you override <code>==</code> <pre><code>def ==(other) return self.weight == other.weight && self.expire_date == other.expire_date end </code></pre> and the loop changes into this <pre><code>arr.each {|c| if h.has_key?(c.name) if problems.has_key?(c.name) problems[c.name]=problems[c.name]<<c elsif h[c.name] != c problems[c.name]=problems[c.name]<<c<<h[c.name] h.delete(c.name) end else h[c.name]=c end } </code></pre> Finally you might want to convert the <code>Hash</code> back to an <code>Array</code> <pre><code>result = h.values </code></pre>
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1. COWOW, thx Jonas ;)
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2. COIt's mostly copy and paste from an old blog post. Also I just corrected a bug.
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3. CODid it solve your problem?
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