title: What does tilde-greater-than (~>) mean in Ruby gem dependencies?
body: <p>What does <code>~&gt;</code> mean in the context of Ruby gem depenedencies?</p>
  
  <p>For example, when opening a legacy project in the RubyMine IDE, I get this
  message</p>
  
  <pre>
  Gems required for project are not attached:
  arel (~> 2.0.2),
  rspec-expectation (~> 2.5.0)...
  </pre>
  
  <p>I've seen this tilde-greater-than notation elsewhere in the Ruby world (it's not
  specific to RubyMine). Does this operator have a name other than the
  awkward-sounding <em>tilde-greater-than</em>?</p>