title: Use From to convert the inner value of a parametric type
body: <p>If I have a parametric type like this:</p>
  <pre><code>struct Outer&lt;A&gt; {
     inner: A,
  }
  </code></pre>
  <p>Is it possible to create an implementation of the <code>From</code> trait for <code>Outer</code> that will convert <code>Outer&lt;A&gt;</code> to <code>Outer&lt;B&gt;</code> if there exists a <code>From</code> that converts <code>A</code> to <code>B</code>?</p>
  <p>Something like this (which doesn't work, as far as I can tell):</p>
  <pre><code>impl&lt;A, B: From&lt;A&gt;&gt; From&lt;Outer&lt;A&gt;&gt; for Outer&lt;B&gt; {
      fn from(oa: Outer&lt;A&gt;) -&gt; Self {
          Outer {
              inner: oa.inner.into(),
          }
      }
  }
  </code></pre>