title: Count, size, length...too many choices in Ruby?
body: <p>I can't seem to find a definitive answer on this and I want to make sure I understand this to the "n'th level"  :-)</p>
  
  <pre>
  
      a = { "a" => "Hello", "b" => "World" }
      a.count  # 2
      a.size   # 2
      a.length # 2
  
      a = [ 10, 20 ]
      a.count  # 2
      a.size   # 2
      a.length # 2
  
  </pre>
  
  <p>So which to use?  If I want to know if a has more than one element then it doesn't seem to matter but I want to make sure I understand the real difference.  This applies to arrays too.  I get the same results.</p>
  
  <p>Also, I realize that count/size/length have different meanings with ActiveRecord.  I'm mostly interested in pure Ruby (1.92) right now but if anyone wants to chime in on the difference AR makes that would be appreciated as well.</p>
  
  <p>Thanks!</p>