title: map(keyPath) where keyPath is a variable
body: <pre><code>let arr = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5)]
  arr.map(\.0) // [1, 2, 3, 4, 5]
  </code></pre>
  <p>Works great. But the below code doesn't compile:</p>
  <pre><code>let keyPath = \(Int, Int).0
  arr.map(keyPath)
  </code></pre>
  <blockquote>
  <p>Cannot convert value of type 'WritableKeyPath&lt;(Int, Int), Int&gt;' to
  expected argument type '((Int, Int)) throws -&gt; T'.<br />
  Generic parameter 'T' could not be inferred.</p>
  </blockquote>