title: Rust Map Syntax Explanation Needed
body: <p>recently started learning Rust and I am having some problems with syntax.
  Can anyone explain to me this line:</p>
  <pre><code>// Stores all the kitties, key is the kitty id / index
  
  pub Kitties get(fn kitties): map hasher(blake2_128_concat) u32 =&gt; Option&lt;Kitty&gt;;
  </code></pre>
  <p>So we're creating here public Kitties(variable) that accepts some function.
  Kitties is of a type map hasher(blake2_128_concat) u32 which returns Option</p>
  <p>map hasher? Also couldn't find hasher in documentation.</p>