title: what does 'T', 'f', 'E', 'e', '→' stand for in dart/flutter docs?
body: <p>i`m learning the flutter, but i do not understand those letters meaning.</p>
  
  <pre><code>map&lt;T&gt;(T f(E e)) → Iterable&lt;T&gt;
  Returns a new lazy Iterable with elements that are created by 
  calling f on each element of this Iterable in iteration order. [...]
  </code></pre>
  
  <p>so,what do they stand for?
  T:
  f:
  E:
  e:
  →:</p>