title: Bidirectional Dict in Julia
body: <p>I have some problem where I need to define a one-to-one mapping from one variable to another. I am using a Dictionary like this:</p>
  <pre><code>mapping = Dict('I'=&gt;1, 'V'=&gt;5, 'X'=&gt;10)
  </code></pre>
  <p>I also want to map it back, so at the moment I define a second Dict:</p>
  <pre><code>inverse_mapping = Dict(1=&gt;'I', 5=&gt;'V', 10=&gt;'X')
  </code></pre>
  <p>Is there a better collection for this out there? something like a two way dictionary or maybe another kind of hash table?</p>