title: Is it possible to declare a type alias inside a trait?
body: <p>Existing syntax allows us to write a default value for associated type:</p>
  <pre class="lang-rust prettyprint-override"><code>trait Foo {
      type Bar = i32;
  }
  </code></pre>
  <p>I want something like C++:</p>
  <pre class="lang-rust prettyprint-override"><code>trait Foo {
      typedef int Bar;
  }
  </code></pre>
  <p>This is not valid Rust code, but tries to show my intention:</p>
  <pre class="lang-rust prettyprint-override"><code>trait Foo&lt;T&gt; {
      trait Trait = Into&lt;T&gt; + /* 10 other traits dependent on T */;
      
      fn foo(x: Type) -&gt; Trait;
  }
  </code></pre>