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copied!<p>At the <a href="http://ruby-doc.org/core-2.0.0/ObjectSpace.html" rel="nofollow"><code>ObjectSpace</code> doc page</a>, note the sentence: "The contents of the returned hash are implementation specific. It may be changed in future." In other words, with <code>ObjectSpace.count_objects</code> you never know, unless you dig deep in the particular Ruby implementation. Let me demonstrate this for you:</p> <pre><code>def sense_changes prev ObjectSpace.count_objects.merge( prev ) { |_, a, b| a - b }.delete_if { |_, v| v == 0 } end prev = ObjectSpace.count_objects # we do absolutely nothing sense_changes( prev ) #=> { :FREE=>-364, :T_OBJECT=>8, :T_STRING=>270, :T_HASH=>11, :T_DATA=>4, :T_MATCH=>11, :T_NODE=>14} </code></pre> <p>And you can keep wondering until the cows come home what the heaven has happened in the <code>ObjectSpace</code> while you have done nothing. As for the <code>:T_CLASS</code> field change by 3, that you observed, Denis's answer applies: 1 is caused by the class itself, 1 by its eigenclass, and 1 by we don't know what (Update: As tlewin has shown, it's the eigenclass's eigenclass). Let me just add that Ruby objects do not have allocated eigenclasses upon creation (Update: As tlewin has shown, classes are an exception to this rule.).</p> <p>Unless you are a core developer, you barely need to wonder about the contents of <code>ObjectSpace.count_objects</code> hash. If you are interested in accessing classes via <code>ObjectSpace</code>, use</p> <pre><code>ObjectSpace.each_object( Class ) </code></pre> <p>Indeed:</p> <pre><code>k = ObjectSpace.each_object( Class ).to_a a = Class.new ObjectSpace.each_object( Class ).to_a.size - k.size #=> 1 ObjectSpace.each_object( Class ).to_a - k == [ a ] #=> true </code></pre>

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